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Commutative Property – Properties & Examples
The word ‘commutative’ is taken from the French word ‘commute,’ which means move around. For the numbers or variables to hold the commutative property, they can move around (within an expression) like a commuter and give the same result when a particular operation is applied to them. Since ancient times, the commutative property was known, but mathematicians started using it at the end of the 18^{th} century.
The commutative property is related to binary operations and functions. If the two elements follow the commutative property under some operation, they are said to be commuted under that particular operation.
What is Commutative Property?
If changing the order of the numbers does not change the result in a certain mathematical expression, then the operation is commutative. Only addition and multiplication are commutative, while subtraction and division are noncommutative.
Commutative Property of Addition
According to the commutative property of addition, if the numbers are added in any order, the result is the same. Suppose that if the number a is added to the number b, and the result is equal to some number p, then if we interchange the positions of a and b, the result is still equal to p i.e.
a + b = b + a = p
The numbers a and b are called addends.
This property also works for more than two numbers i.e.
a + b + c + d = d + c + b + a
Example 1
Show that the following numbers obey the commutative property of addition:
2, 4, 6, and 9
2 + 4 + 6 + 9 = 21
9 + 6 + 4 + 2 = 21
The result is same in both cases. Hence,
2 + 4 + 6 + 9 = 9 + 6 + 4 + 2
The real-life example is that if you want to conduct a survey in your society regarding the number of children in each house, you can start from any house and count the number of children in every house and total them. The order of house is not important here.
The other real-life examples are wearing pair of gloves, pair of shoes, and pair of socks are examples of commutative property.
Commutative Property of Multiplication
According to the commutative property of multiplication, if the numbers are multiplied in any order, the result is the same. Suppose that if the number a is multiplied with the number b, and the result is equal to some number q, then if we interchange the positions of a and b, the result is still equal to q i.e.
a × b = b × a = q
This property also works for more than two numbers i.e.
a × b × c × d = d × c × b × a
Compositions of functions and matrix multiplication are also not commutative.
Example 2
Show that the following numbers obey the commutative property of multiplication:
2, 4, 6, and 9
2 × 4 × 6 × 9 = 432
9 × 6 × 4 × 2 = 432
The result is the same in both cases. Hence,
2 × 4 × 6 × 9 = 9 × 6 × 4 × 2
Why Subtraction and Division are Noncommutative?
To understand why subtraction and division do not follow the commutative rule, follow the examples below.
Example 3
State whether the following expression is true.
a – b = b – a
- Step 1: What you need to show?
a – b = b – a
- Step 2: Take the left-hand side and try to prove it equal to the right-hand side.
a – b
- Step 3: Take -1 common.
–1 (– a + b) = – (– a + b)
- Step 4: Reverse the addends.
– (b – a)
- Step 5: See if you get the desired result.
a – b = – (b – a)
- Step 6: State your findings.
Since,
a – b = – (b – a)
Hence,
a – b ≠ b – a
Therefore, the given expression is false and does not follow the commutative property.
Example 4
State whether the following expression is true.
2a ÷ a = a ÷ 2a
- Step 1: What you need to show?
2a ÷ a = a ÷ 2a
- Step 2: Take the left-hand side.
2a ÷ a
- Step 3: Solve.
2a ÷ a = 2
- Step 4: Solve the right-hand side now.
a ÷ 2a = 1/2
- Step 5: State your findings.
Since,
2a ÷ a = 2
a ÷ 2a = 1/2
Hence,
2a ÷ a ≠ a ÷ 2a
Therefore, the given expression is false and does not follow the commutative property.
Practice Problems
- Which of the following follows the commutative law?
- 9 + 12
- –7 × 6
- 72 ÷ 5
- –99 – 7
Answer:
- Yes b. Yes c. No d. Yes
- The table below shows the pocket money of 4 students.
Student | A | B | C | D |
Pocket Money (in $) | 14 | 7 | x | 2 x |
If the sum of pocket money of students A and B is equal to the sum of pocket money of students C and D, find the value of x.
Answer: 7
- Show that 12% of 25 is the same as 25% of 12.
- There are two areas of car parking in the basement. In area A, cars are parked in such a way that there are 6 cars parked each in 12 rows, while in area B, there are 12 cars parked each in the remaining 6 rows. How many cars are there in the parking lot?
Answer: 144
- Sam brings home 4 crates of bottles. Each crate has 8 rows of bottles, where each row can hold 6 bottles. How many bottles did Sam buy?
Answer: 192
- Nina made 8 cookies and distributed them among 4 friends. Liza made 4 cookies and distributed them among 8 friends. Is this division of cookies obey the commutative law?
Answer: No, commutative law is not true for division, i.e., 8/4 ≠ 4/8
- In the morning, Ali spends 10 minutes in the washroom, 12 minutes in breakfast, and 7 minutes in changing before he goes for school. On the other hand, James spends 7 minutes in the washroom, 12 minutes in breakfast, and 10 minutes in getting ready before he goes for school.
Is the overall time taken by Ali and James in getting ready is equal?
Answer: Yes