Order of operations

Short description: Performing order of mathematical operations

In mathematics and computer programming, the order of operations is a collection of rules that reflect conventions about which operations to perform first in order to evaluate a given mathematical expression.

These rules are formalized with a ranking of the operators. The rank of an operator is called its precedence, and an operation with a higher precedence is performed before operations with lower precedence. Calculators generally perform operations with the same precedence from left to right,[1] but some programming languages and calculators adopt different conventions.

For example, multiplication is granted a higher precedence than addition, and it has been this way since the introduction of modern algebraic notation.[2][3] Thus, in the expression 1 + 2 × 3, the multiplication is performed before addition, and the expression has the value 1 + (2 × 3) = 7, and not (1 + 2) × 3 = 9. When exponents were introduced in the 16th and 17th centuries, they were given precedence over both addition and multiplication and placed as a superscript to the right of their base.[2] Thus 3 + 52 = 28 and 3 × 52 = 75.

These conventions exist to avoid notational ambiguity while allowing notation to remain brief.[4] Where it is desired to override the precedence conventions, or even simply to emphasize them, parentheses ( ) can be used. For example, (2 + 3) × 4 = 20 forces addition to precede multiplication, while (3 + 5)2 = 64 forces addition to precede exponentiation. If multiple pairs of parentheses are required in a mathematical expression (such as in the case of nested parentheses), the parentheses may be replaced by brackets or braces to avoid confusion, as in [2 × (3 + 4)] − 5 = 9.

These rules are meaningful only when the usual notation (called infix notation) is used. When functional or Polish notation are used for all operations, the order of operations results from the notation itself.

Internet memes sometimes present ambiguous infix expressions that cause disputes and increase web traffic.[5][6] Most of these ambiguous expressions involve mixed division and multiplication, where there is no general agreement about the order of operations.

## Contents

* 1 Definition
* 1.1 Examples
* 2 Mnemonics
* 3 Special cases
* 3.1 Serial exponentiation
* 3.2 Unary minus sign
* 3.3 Mixed division and multiplication
* 4 Calculators
* 5 Programming languages
* 6 See also
* 7 Notes
* 8 References
* 9 Further reading

## Definition

The order of operations, that is, the order in which the operations in an expression are usually performed, results from a convention adopted throughout mathematics, science, technology and many computer programming languages. It is summarized as:[2][7][8]

1. Parentheses
2. Exponentiation
3. Multiplication and Division
4. Addition and Subtraction

This means that to evaluate an expression, one first evaluates any sub-expression inside parentheses, working inside to outside if there is more than one set. Whether inside parenthesis or not, the operator that is higher in the above list should be applied first.

The commutative and associative laws of addition and multiplication allow adding terms in any order, and multiplying factors in any order—but mixed operations obey the standard order of operations.

In some contexts, it is helpful to replace a division with multiplication by the reciprocal (multiplicative inverse) and a subtraction by addition of the opposite (additive inverse). For example, in computer algebra, this allows one to handle fewer binary operations, and makes it easier to use commutativity and associativity when simplifying large expressions (for more, see Computer algebra § Simplification). Thus 3 ÷ 4 = 3 × ⁠1/4⁠; in other words, the quotient of 3 and 4 equals the product of 3 and ⁠1/4⁠. Also 3 − 4 = 3 + (−4); in other words the difference of 3 and 4 equals the sum of 3 and −4. Thus, 1 − 3 + 7 can be thought of as the sum of 1 + (−3) + 7, and the three summands may be added in any order, in all cases giving 5 as the result.

The root symbol √ is traditionally prolongated by a bar (called vinculum) over the radicand (this avoids the need for parentheses around the radicand). Other functions use parentheses around the input to avoid ambiguity.[9][10][lower-alpha 1] The parentheses can be omitted if the input is a single numerical variable or constant,[2] as in the case of sin x = sin(x) and sin π = sin(π).[lower-alpha 1] Another shortcut convention that is sometimes used is when the input is monomial; thus, sin 3x = sin(3x) rather than (sin(3)) x, but sin x \+ y = sin(x) + y, because x \+ y is not a monomial. This, however, is ambiguous and not universally understood outside of specific contexts.[lower-alpha 2] Some calculators and programming languages require parentheses around function inputs, some do not.

Symbols of grouping can be used to override the usual order of operations.[2] Grouped symbols can be treated as a single expression.[2] Symbols of grouping can be removed using the associative and distributive laws, also they can be removed if the expression inside the symbol of grouping is sufficiently simplified so no ambiguity results from their removal.

### Examples

Multiplication before addition:

1+2×3=1+6=7.

Parenthetic subexpressions are evaluated first:

(1+2)×3=3×3=9.

Exponentiation before multiplication, multiplication before subtraction:

1−2×34=1−2×81=1−162=−161.

When an expression is written as a superscript, the superscript is considered to be grouped by its position above its base:

1+23+4=1+27=1+128=129, while by contrast, `1 + 2 ** 3 + 4` e.g. in a Python program, evaluates to 1+8+4=13.

The operand of a root symbol is determined by the overbar:

1+3+5=4+5=2+5=7.

A horizontal fractional line also acts as a symbol of grouping:

1+23+4+5=37+5.

For ease in reading, other grouping symbols, such as curly braces { } or square brackets [ ], are sometimes used along with parentheses ( ). For example:

([1+2]÷[3+4])+5=(3÷7)+5

## Mnemonics

Mnemonics are often used to help students remember the rules, involving the first letters of words representing various operations.[11][12][13]

* The acronym PEMDAS is common in the United States[14] and France.[15] It stands for Parentheses, Exponents, Multiplication/Division, Addition/Subtraction.[16] PEMDAS is often expanded to the mnemonic "Please Excuse My Dear Aunt Sally" in schools.[17]
* BEDMAS, standing for Brackets, Exponents, Division/Multiplication, Addition/Subtraction is common in Canada and New Zealand.[18]
* Other countries, such as the UK,[18] may use BODMAS meaning Brackets, Operations, Division/Multiplication, Addition/Subtraction. Sometimes the O is expanded as "Of"[lower-alpha 3] or "Order" (i.e. powers/exponents or roots).[19][20][21]
* BIDMAS is also used, standing for Brackets, Indices, Division/Multiplication, Addition/Subtraction.[22]
* In Germany, the convention is simply taught as Punktrechnung vor Strichrechnung.

These mnemonics may be misleading when written this way.[23][17] For example, misinterpreting any of the above rules to mean "addition first, subtraction afterward" would incorrectly evaluate the expression[17] a−b+c as a−(b+c), while the correct evaluation is (a−b)+c. These values are different when c≠0.

6÷2(1+2) is interpreted as 6÷(2×(1+2)) by a fx-82MS (upper), and (6÷2)×(1+2) by a TI-83 Plus calculator (lower), respectively.

The "Addition/Subtraction" in the mnemonics should be interpreted as that subtraction is addition of the opposite, while the expression  a ÷ b × c is ambiguous and can be read multiple ways since (a÷b)×c is different from a÷(b×c) when c≠±1. Additional ambiguities caused by the use of multiplication by juxtaposition and using the slash to represent division are discussed below. In general, the surest way to avoid ambiguity is to use parentheses.

## Special cases

### Serial exponentiation

If exponentiation is indicated by stacked symbols using superscript notation, the usual rule is to work from the top down:[24][2][10][25]

abc = a(bc)

which typically is not equal to (ab)c. This convention is useful because there is a property of exponentiation that (ab)c = abc, so it's unnecessary to use serial exponentiation for this.

However, when using operator notation with a caret (^) or arrow (↑), there is no common standard.[26] For example, Microsoft Excel and computation programming language MATLAB evaluate `a^b^c` as (ab)c, but Google Search and Wolfram Alpha as a(bc). Thus `4^3^2` is evaluated to 4,096 in the first case and to 262,144 in the second case.

### Unary minus sign

There are differing conventions concerning the unary operator − (usually read "minus"). In written or printed mathematics, the expression −32 is interpreted to mean −(32) = −9.[2][27]

In some applications and programming languages, notably Microsoft Excel, PlanMaker (and other spreadsheet applications) and the programming language bc, unary operators have a higher priority than binary operators, that is, the unary minus has higher precedence than exponentiation, so in those languages −32 will be interpreted as (−3)2 = 9.[28] This does not apply to the binary minus operator −; for example in Microsoft Excel while the formulas `=−2^2`, `=-(2)^2` and `=0+−2^2` return 4, the formulas `=0−2^2` and `=−(2^2)` return −4.

### Mixed division and multiplication

In fields of science such as physics, engineering, and academic literature, as well as in educational institutes in most of the world, multiplication denoted by juxtaposition (also known as implied multiplication) is interpreted as having higher precedence than division, so that 1 ÷ 2n equals 1 ÷ (2n).[2] For example, the manuscript submission instructions for the Physical Review journals state that multiplication is of higher precedence than division,[29] and this is also the convention observed in prominent physics textbooks such as the Course of Theoretical Physics by Landau and Lifshitz and the Feynman Lectures on Physics.[lower-alpha 4] However, schools in the United States teach that implicit multiplication is identical to explicit multiplication such that 1÷2n is deemed the same as writing 1 ÷ 2 * n.[30]

This ambiguity is often exploited in internet memes such as "8÷2(2+2)", for which there are two conflicting interpretations: 8÷[2(2+2)] = 1 and [8÷2](2+2) = 16.[31] The expression "6÷2(1+2)" also gained notoriety in the exact same manner, with the two interpretations resulting in the answers 1 and 9.[32]

Ambiguity can also be caused by the use of the slash symbol, '/', for division. The Physical Review submission instructions suggest to avoid expressions of the form a/b/c; ambiguity can be avoided by instead writing (a/b)/c or a/(b/c).[29]

## Calculators

Different calculators follow different orders of operations.[2] Many simple calculators without a stack implement chain input, working left to right without any priority given to different operators, give a different result from that given by more sophisticated calculators. For example, on a simple calculator, typing `1 + 2 × 3 =` yields 9, while a more sophisticated calculator will use a more standard priority, so typing `1 + 2 × 3 =` yields 7.

The Microsoft Calculator program uses the former in its standard view and the latter in its scientific and programmer views.

Chain input expects two operands and an operator. When the next operator is pressed, the expression is immediately evaluated and the answer becomes the left hand of the next operator. Advanced calculators allow entry of the whole expression, grouped as necessary, and evaluates only when the user uses the equals sign.

Calculators may associate exponents to the left or to the right. For example, the expression `a^b^c` is interpreted as a(bc) on the TI-92 and the TI-30XS MultiView in "Mathprint mode", whereas it is interpreted as (ab)c on the TI-30XII and the TI-30XS MultiView in "Classic mode".

An expression like `1/2x` is interpreted as 1/(2x) by TI-82,[3] as well as many modern Casio calculators[33] (configurable on some like the fx-9750GIII[34]), but as (1/2)x by TI-83 and every other TI calculator released since 1996,[35][3] as well as by all Hewlett-Packard calculators with algebraic notation. While the first interpretation may be expected by some users due to the nature of implied multiplication,[36] the latter is more in line with the rule that multiplication and division are of equal precedence.[3]

When the user is unsure how a calculator will interpret an expression, parentheses can be used to remove the ambiguity.[3]

Order of operations arose due to the adaptation of infix notation in standard mathematical notation, which can be notationally ambiguous without such conventions, as opposed to postfix notation or prefix notation, which do not need orders of operations.[37][38] Hence, calculators utilizing Reverse Polish notation (RPN) using a stack to enter expressions in the correct order of precedence do not need parentheses or any possibly model-specific order of execution.[17][16]

## Programming languages

Most programming languages use precedence levels that conform to the order commonly used in mathematics,[39][26] though others, such as APL, Smalltalk, Occam and Mary, have no operator precedence rules (in APL, evaluation is strictly right to left; in Smalltalk, it is strictly left to right).

Furthermore, because many operators are not associative, the order within any single level is usually defined by grouping left to right so that `16/4/4` is interpreted as (16/4)/4 = 1 rather than 16/(4/4) = 16; such operators are referred to as "left associative". Exceptions exist; for example, languages with operators corresponding to the cons operation on lists usually make them group right to left ("right associative"), e.g. in Haskell, `1:2:3:4:[] == 1:(2:(3:(4:[]))) == [1,2,3,4]`.

Dennis Ritchie, creator of the C language, said of the precedence in C (shared by programming languages that borrow those rules from C, for example, C++, Perl and PHP) that it would have been preferable to move the bitwise operators above the comparison operators.[40] Many programmers have become accustomed to this order, but more recent popular languages like Python[41] and Ruby[42] do have this order inversed. The relative precedence levels of operators found in many C-style languages are as follows:

1 | ()  []  -> .  :: | Function call, scope, array/member access

|
|

2 | !  ~  \-  \+  *  & sizeof type cast ++  \--  | (most) unary operators, sizeof and type casts (right to left)
3 | *  /  % MOD | Multiplication, division, modulo
4 | \+  - | Addition and subtraction
5 | << >> | Bitwise shift left and right
6 | < <=  > >= | Comparisons: less-than and greater-than
7 | ==  != | Comparisons: equal and not equal
8 | & | Bitwise AND
9 | ^ | Bitwise exclusive OR (XOR)
10 | | | Bitwise inclusive (normal) OR
11 | && | Logical AND
12 | || | Logical OR
13 | ? : | Conditional expression (ternary)
14 | =  +=  -=  *=  /=  %=  &=  |=  ^=  <<=  >>= | Assignment operators (right to left)
15 | , | Comma operator
Simplified formal grammar for arithmetitical expressions in a programming language (left),[43] and derivation of the example expression `(a+b)^2/2` (right). The latter corresponds to a hierarchical structure ("syntax tree") which is unique for the given expression. The compiler generates machine code from the tree in such a way that operations originating at the lowest hierarchy level are executed first.

Examples:

* `!A + !B` is interpreted as `(!A) + (!B)`
* `++A + !B` is interpreted as `(++A) + (!B)`
* `A + B * C` is interpreted as `A + (B * C)`
* `A || B && C` is interpreted as `A || (B && C)`
* `A && B == C` is interpreted as `A && (B == C)`
* `A & B == C` is interpreted as `A & (B == C)`

(In Python, Ruby, PARI/GP and other popular languages, `A & B == C` is interpreted as `(A & B) == C`.)

Source-to-source compilers that compile to multiple languages need to explicitly deal with the issue of different order of operations across languages. Haxe for example standardizes the order and enforces it by inserting brackets where it is appropriate.[44]

The accuracy of software developer knowledge about binary operator precedence has been found to closely follow their frequency of occurrence in source code.[45]

## See also

* Common operator notation (for a more formal description)
* Hyperoperation
* Logical connective
* Operator associativity
* Operator overloading
* Operator precedence in C and C++
* Polish notation
* Reverse Polish notation

## Notes

1. ↑ 1.0 1.1 Some authors deliberately avoid any omission of parentheses with functions even in the case of single numerical variable or constant arguments (i.e. Oldham in Atlas), whereas other authors (like NIST) apply this notational simplification only conditionally in conjunction with specific multi-character function names (like `sin`), but don't use it with generic function names (like `f`).
2. ↑ To avoid any ambiguity, this notational simplification for monomials is deliberately avoided in works such as Oldham's Atlas of Functions or the NIST Handbook of Mathematical Functions.
3. ↑ "Of" when used to mean a mathematical operation means multiplication. For example "half of fifty" is understood to mean "1/2 times 50", which equals 25.
4. ↑ For example, the third edition of Mechanics by Landau and Lifshitz contains expressions such as hPz/2π (p. 22), and the first volume of the Feynman Lectures contains expressions such as 1/2√N (p. 6–7). In both books, these expressions are written with the convention that the solidus is evaluated last. This also implies that an expression like 8/2(4) has solution 1 as the omission of the multiplication sign (x * or .) implies that the solidus is evaluated last even if positioned more to the left.

## References

1. ↑ "Calculation operators and precedence: Excel for Microsoft 365, Excel for Microsoft 365 for Mac, Excel for the web, Excel 2021, Excel 2021 for Mac, Excel 2019, Excel 2019 for Mac, Excel 2016, Excel 2016 for Mac". Microsoft Support. Microsoft. 2023. https://support.microsoft.com/en-us/office/calculation-operators-and-precedence-36de9366-46fe-43a3-bfa8-cf6d8068eacc.
2. ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 "2.4.1.1. Definition arithmetischer Ausdrücke". written at Leipzig, Germany (in de). Taschenbuch der Mathematik. 1. Weiß, Jürgen (23 ed.). Thun, Switzerland / Frankfurt am Main, Germany: Verlag Harri Deutsch (and B. G. Teubner Verlagsgesellschaft, Leipzig). 1987. pp. 115–120, 802. ISBN 3-87144-492-8. "Regel 7: Ist F(A) Teilzeichenreihe eines arithmetischen Ausdrucks oder einer seiner Abkürzungen und F eine Funktionenkonstante und A eine Zahlenvariable oder Zahlenkonstante, so darf F A dafür geschrieben werden. [Darüber hinaus ist noch die Abkürzung Fn(A) für (F(A))n üblich. Dabei kann F sowohl Funktionenkonstante als auch Funktionenvariable sein.]"
3. ↑ 3.0 3.1 3.2 3.3 3.4 "Order of Operations: Why?". The Math Doctors. 2019-09-30. https://www.themathdoctors.org/order-of-operations-why/none ; "Order of Operations: Why These Rules?". The Math Doctors. 2019-10-03. https://www.themathdoctors.org/order-of-operations-why-these-rules/none ; "Order of Operations: Subtle Distinctions". The Math Doctors. 2019-10-07. https://www.themathdoctors.org/order-of-operations-subtle-distinctions/none ; "Order of Operations: Fractions, Evaluating, and Simplifying". The Math Doctors. 2019-10-10. https://www.themathdoctors.org/order-of-operations-fractions-evaluating-and-simplifying/none ; "Order of Operations: Implicit Multiplication?". The Math Doctors. 2019-10-14. https://www.themathdoctors.org/order-of-operations-implicit-multiplication/none ; "Order of Operations: Historical Caveats". The Math Doctors. 2019-10-17. https://www.themathdoctors.org/order-of-operations-historical-caveats/.
4. ↑ Fundamentals of Algebra and Trigonometry (4 ed.). Boston, Massachusetts, USA: Prindle, Weber & Schmidt, Incorporated. 1978. ISBN 0-87150-252-6. https://books.google.com/books?id=bZdfLRHFGw8C. Retrieved 2023-09-17. "The language of algebra […] may be used as shorthand, to abbreviate and simplify long or complicated statements."
5. ↑ "What Is the Answer to That Stupid Math Problem on Facebook? And why are people so riled up about it?". 2013-03-12. https://slate.com/technology/2013/03/facebook-math-problem-why-pemdas-doesnt-always-give-a-clear-answer.html.
6. ↑ "48÷2(9+3) = ?". 2017-07-20. https://knowyourmeme.com/memes/48293.
7. ↑ "Precedence". https://mathworld.wolfram.com/Precedence.html.
8. ↑ "The Order of Operations: PEMDAS". https://www.purplemath.com/modules/orderops.htm.
9. ↑ An Atlas of Functions: with Equator, the Atlas Function Calculator (2 ed.). Springer Science+Business Media, LLC. 2009. doi:10.1007/978-0-387-48807-3. ISBN 978-0-387-48806-6.
10. ↑ 10.0 10.1 Olver, Frank W. J.; Lozier, Daniel W.; Boisvert, Ronald F. et al., eds (2010). NIST Handbook of Mathematical Functions. National Institute of Standards and Technology (NIST), U.S. Department of Commerce, Cambridge University Press. ISBN 978-0-521-19225-5. [1]
11. ↑ "Rules of arithmetic". 2009. http://www.mathcentre.ac.uk/resources/uploaded/mc-ty-rules-2009-1.pdf. (9 pages)
12. ↑ "Please Excuse My Dear Aunt Sally (PEMDAS)--Forever!". Education Week - Coach G's Teaching Tips. 2011-01-01. http://blogs.edweek.org/teachers/coach_gs_teaching_tips/2011/01/math_teachers_please_excuse_dear_aunt_sally--forever.html.
13. ↑ "What is PEMDAS? - Definition, Rule & Examples". Study.com. 2021-09-22. http://study.com/academy/lesson/what-is-pemdas-definition-rule-examples.html.
14. ↑ "Developing Students' Mathematical Skills Involving Order of Operations". International Journal of Research in Education and Science (IJRES) (University of Brunei Darussalam) 3 (2): 373-382. Summer 2017. doi:10.21890/ijres.327896. ISSN 2148-9955. https://files.eric.ed.gov/fulltext/EJ1148460.pdf. Retrieved 2023-11-19. "The PEMDAS is an acronym or mnemonic for the order of operations that stands for Parenthesis, Exponents, Multiplication, Division, Addition and Subtraction. This acronym is widely used in the United States of America. Meanwhile, in other countries such as United Kingdom and Canada, the acronyms used are BODMAS (Brackets, Order, Division, Multiplication, Addition and Subtraction) and BIDMAS (Brackets, Indices, Division, Multiplication, Addition and Subtraction).". (11 pages)
15. ↑ "Le calcul qui divise : 6÷2(1+2) - Micmaths" (in fr). https://www.youtube.com/watch?v=tYf3CpbqAVo. Archived at Ghostarchive and the Wayback Machine
16. ↑ 16.0 16.1 Order of Operations and RPN (Expository paper). Master of Arts in Teaching (MAT) Exam Expository Papers. Lincoln, Nebraska, USA: University of Nebraska. July 2007. Paper 46. https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1045&context=mathmidexppap. Retrieved 2020-06-14.
17. ↑ 17.0 17.1 17.2 17.3 Algorithms for RPN calculators (1 ed.). Cambridge, Massachusetts, USA: Wiley-Interscience, John Wiley & Sons, Inc.. 1978. p. 31. ISBN 0-471-03070-8. https://archive.org/details/algorithmsforrpn0000ball.
18. ↑ 18.0 18.1 "Order of Operations PEMDAS". 2023. https://www.mathsisfun.com/operation-order-pemdas.html. "In the UK they say BODMAS (Brackets, Orders, Divide, Multiply, Add, Subtract). In Canada they say BEDMAS (Brackets, Exponents, Divide, Multiply, Add, Subtract)."
19. ↑ "What Is BODMAS And BIDMAS? Explained For Teachers". 2023-08-30. https://thirdspacelearning.com/us/blog/what-is-bodmas/.
20. ↑ "Order of operations" (DOC). http://syllabus.bos.nsw.edu.au/assets/global/files/maths_s3_sampleu1.doc.
21. ↑ "Bodmas Rule - What is Bodmas Rule - Order of Operations". https://www.vedantu.com/maths/bodmas-rule.
22. ↑ "Higher Priorities". Mathematics in School (UK: Mathematical Association) 37 (3): 17. May 2008. doi:10.2307/30216129. ISSN 0305-7259. https://www.researchgate.net/profile/Colin-Foster-4/publication/261812399_Higher_Priorities/links/556878c708aefcb861d4bff6/Higher-Priorities.pdf. Retrieved 2023-08-30. (1 page)
23. ↑ "Exploring Mathematical Reasoning of the Order of Operations: Rearranging the Procedural Component PEMDAS". Journal of Mathematics Education at Teachers College (Program in Mathematics and Education Teachers College, Columbia University, in the City of New York) 4 (2): 73–78. Fall–Winter 2013. doi:10.7916/jmetc.v4i2.633. ISSN 2156-1397. https://journals.library.columbia.edu/index.php/jmetc/article/download/633/79. Retrieved 2013-08-23. ""[…] students frequently make calculation errors with expressions which have either multiplication and division or addition and subtraction next to each other. […]". (iv+6 pages)
24. ↑ "A report on primes of the form k · 2n \+ 1 and on factors of Fermat numbers". Proceedings of the American Mathematical Society (University of California, Berkeley, California, USA) 9 (5): 673–681 [677]. October 1958. doi:10.1090/s0002-9939-1958-0096614-7. https://www.ams.org/journals/proc/1958-009-05/S0002-9939-1958-0096614-7/S0002-9939-1958-0096614-7.pdf. Retrieved 2020-06-28. (9 pages)
25. ↑ Zeidler, Eberhard, ed (2013) (in de). Springer-Handbuch der Mathematik I. I (1 ed.). Berlin / Heidelberg, Germany: Springer Spektrum, Springer Fachmedien Wiesbaden. p. 590. doi:10.1007/978-3-658-00285-5. ISBN 978-3-658-00284-8. (xii+635 pages)
26. ↑ 26.0 26.1 "Exponentiation Associativity and Standard Math Notation". Codeplea - Random thoughts on programming. 2016-08-23. https://codeplea.com/exponentiation-associativity-options.
27. ↑ Elementary Algebra for College Students (8 ed.). Prentice Hall PTR. 2010-01-13. Chapter 1, Section 9, Objective 3. ISBN 978-0-321-62093-4.
28. ↑ "Formula Returns Unexpected Positive Value". Microsoft. 2005-08-15. https://support.microsoft.com/en-gb/kb/kbview/132686.
29. ↑ 29.0 29.1 "Physical Review Style and Notation Guide". American Physical Society. Section IV-E-2-e. https://publish.aps.org/files/styleguide-pr.pdf.
30. ↑ Cite error: Invalid `<ref>` tag; no text was provided for refs named `Paradox`
31. ↑ "This equation has 2 wildly different answers depending on what you learned in school, and it's dividing the internet" (in en-US). https://www.insider.com/viral-math-problem-solution-dividing-the-internet-2019-7.
32. ↑ "What Is 6÷2(1+2) = ? Mathematician Explains The Correct Answer" (in en-US). https://mindyourdecisions.com/blog/2016/08/31/what-is-6÷212-the-correct-answer-explained/.
33. ↑ "Calculation Priority Sequence". Casio. https://support.casio.com/global/en/calc/manual/fx-82MS_85MS_220PLUS_300MS_350MS_en/technical_informatoin/sequence.html.
34. ↑ critor (2021-06-21). "fx-9750GIII vs fx-9860GIII". UCF. https://community.casiocalc.org/topic/8085-fx-9750giii-vs-fx-9860giii/#entry63823. "[…] On the fx-9750GIII, there are 3 possible settings instead of 2 for Input/Output: […] You've also got an additional setting to turn implicit multiplications on/off: […] Imp Multi On […]"
35. ↑ "Implied Multiplication Versus Explicit Multiplication on TI Graphing Calculators". Texas Instruments. 2011-01-16. http://epsstore.ti.com/OA_HTML/csksxvm.jsp?nSetId=103110.
36. ↑ Announcing the TI Programmable 88!. Texas Instruments. 1982. http://www.datamath.net/Leaflets/TI-88_Announcement.pdf. Retrieved 2017-08-03. "Now, implied multiplication is recognized by the AOS and the square root, logarithmic, and trigonometric functions can be followed by their arguments as when working with pencil and paper." (NB. The TI-88 only existed as a prototype and was never released to the public.)
37. ↑ "Łukasiewicz's Parenthesis-Free or Polish Notation". Stanford Encyclopedia of Philosophy. The Metaphysics Research Lab, Department of Philosophy, Stanford University. 2021. https://plato.stanford.edu/entries/lukasiewicz/polish-notation.html. Retrieved 2022-03-26.
38. ↑ "On some properties of reverse Polish Notation". Filomat (Faculty of Sciences and Mathematics, University of Nis) 13: 157–172. 1999. ISSN 0354-5180. (16 pages)
39. ↑ "Operator Precedence". Henderson's Encyclopedia of Computer Science and Technology (Revised ed.). New York, USA: Facts On File, Inc. / Infobase Publishing. 2009. p. 355. ISBN 978-0-8160-6382-6. https://books.google.com/books?id=3Tla6d153uwC&pg=PA355. Retrieved 2023-09-17.
40. ↑ "The Development of the C Language". History of Programming Languages (2 ed.). ACM Press. 1996. https://www.bell-labs.com/usr/dmr/www/chist.html.
41. ↑ "6. Expressions". https://docs.python.org/3/reference/expressions.html.
42. ↑ "precedence - RDoc Documentation". https://ruby-doc.org/3.3.0/syntax/precedence_rdoc.html.
43. ↑ Naur, Peter, ed (1963). ﻿Revised Report on the Algorithmic Language Algol 60﻿ (Report). https://www.masswerk.at/algol60/report.htm. Retrieved 2023-09-17. (CACM Vol. 6 pp. 1–17; The Computer Journal, Vol. 9, p. 349; Numerische Mathematik, Vol. 4, p. 420.)
44. ↑ "6÷2(1+2)=?". Andy Li's Blog. 2011-05-02. http://blog.onthewings.net/2011/05/02/six-divided-by-two-bracket-one-plus-two/.
45. ↑ "Developer beliefs about binary operator precedence". CVu (Farnborough, Hants, UK: Knowledge Software, Ltd.) 18 (4): 14–21. 2008. http://www.knosof.co.uk/cbook/accu06.html. Retrieved 2023-09-17. [2][3][4]

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## Further reading

* A History of Mathematical Notations. Chicago, Illinois, USA / New York, USA: Open Court Publishing / Dover Publications. 1993. ISBN 0-486-67766-4.
* The Development of Logic. Oxford, Oxfordshire, UK: Clarendon Press. 1962. ISBN 0-19-824773-7.
* "Introduction to Scientific Programming - Computational Problem Solving using Maple and C - Operator Precedence Worksheet". Department of Computer Science, University of Utah. 1997. http://www.cs.utah.edu/~zachary/isp/worksheets/operprec/operprec.html.
* "Introduction to Scientific Programming - Computational Problem Solving using Mathematica and C - Operator Precedence Notebook". Department of Computer Science, University of Utah. 1997. http://www.cs.utah.edu/~zachary/ispmma/notebooks/operprec/operprec.html.
* "The Order of Operations". MathSteps: What is it?. Houghton Mifflin Company. 1999. http://eduplace.com/math/mathsteps/4/a/index.html.
* ""Order of operations" and other oddities in school mathematics". Berkeley, California, USA: Department of Mathematics, University of California. 2007-09-13. https://math.berkeley.edu/~wu/order5.pdf. (11 pages)
* "Order of arithmetic operations; in particular, the 48/2(9+3) question.". Department of Mathematics, University of California. 2013-02-21. https://math.berkeley.edu/~gbergman/misc/numbers/ord_ops.html.
* (in de) Keller, Stack und automatisches Gedächtnis – eine Struktur mit Potenzial (Tagungsband zum Kolloquium 14. November 2014 in Jena). GI Series: Lecture Notes in Informatics (LNI) – Thematics. T-7. Bonn, Germany: Gesellschaft für Informatik (GI) / Köllen Druck + Verlag GmbH. 2015. ISBN 978-3-88579-426-4. https://dl.gi.de/bitstream/handle/20.500.12116/4381/lni-t-7.pdf?sequence=1&isAllowed=y. Retrieved 2020-04-12. [5] (77 pages)
* "Implied Multiplication 1: Not as Bad as You Think". The Math Doctors. 2023-08-18. https://www.themathdoctors.org/implied-multiplication-1-not-as-bad-as-you-think/none ; "Implied Multiplication 2: Is There a Standard?". The Math Doctors. 2023-08-25. https://www.themathdoctors.org/implied-multiplication-2-is-there-a-standard/none ; "Implied Multiplication 3: You Can't Prove It". The Math Doctors. 2023-09-01. https://www.themathdoctors.org/implied-multiplication-3-you-cant-prove-it/.

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1. ↑ Linkletter, David (Jun 2018). "The PEMDAS Paradox". p. 6-7. https://archive.org/details/pemdas-paradox-v-1-manuscript.

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