Maths Topic 06 - Inverse operations


Inverse Operations is a maths skill that is commonly tested in 11 plus exams and UK selective tests.

Examples

Inverse operations in sums

Inverse operations are the opposites: Addition and subtraction are opposites & multiplication and division are opposites.

Example Question 1:

4579 + ___ = 4596

Answer: The missing value is 17.

Explanation: To find the answer do the inverse operation, which is to subtract, so 4596 – 4579= 17. 

Example Question 2:

___ – 348 = 45

Answer: The missing value is 393.

Explanation: To find the answer do the inverse operation, which is to add, so 348 + 45 = 393. 

Example Question 3:

___ x 23 = 207

Answer: The missing value is 9.

Explanation: To find the answer do the inverse operation, which is to divide, so 207 divided by 23 = 9. 

Example Question 4:

___ ÷ 3 = 103

Answer: The missing value is 309.

Explanation: To find the answer do the inverse operation, which is to multiply, so 103 x 3 = 309. 

Inverse operations in algebra

To calculate the value of a letter in equations you will need to do an inverse operation on the number, letter or both.

Example Question 5:

Find the value of x if 3x + 3 = 18.

Answer: x = 5

Explanation: Move the 3 to the other side of the equation and the +3 becomes -3. 3x = 18 – 3 which is 15, 3x = 15, so x = 5

Example Question 6:

Find the value of a if 3a + 7 = 21 + a

Answer: a = 7

Explanation: Move the +7 to the right of the equation to join with the 21. The +7 becomes -7. Also move the +a to the left of the equation to join with the 3a. The +a becomes -a so 3a – a = 21 – 7. Do the sums on each side 2a = 14, so a = 7.

Video Tutorials

Inverse of Multiplication

 

Inverse of Addition