Inverse Operations

Suggested Grade Level: 5th or 6th

This would be usable in fifth or sixth grade to introduce the concept of inverse operations. It is the introduction only.

Show the following pictures:

An inverse is an operation that undoes or reverses another operation.

Standing upright reverses standing on your hands and standing on your hand reverses standing up. Also, kneeling down reverses standing upright, and standing upright reverses kneeling down.

Adding something reverses taking it away and taking it away reverses adding. So + and - are inverse operations.

Likewise multiplication and division are inverse operations.

Exercises 1 (Let / represent the division sign.) These are to be done in class on the overhead with the teacher guiding the students to come up with the answers.

1. 3 times 7 divided by 7 = _________ 2. 20 + 13-13= ________3. 35 +6 X 5-35/5= ________ 4. 315 X 25 + 255/315 -255 = ________

Exercise 2: Write your favorite number down. Then follow the steps below.

Add 7, multiply by 10,, divide by 2, add 1000, subtract 20 ,add 3, multiply by 2, subtract 7, divide by 10, subtract 500, subtract 480 = _______ .

(Your answer should be your favorite number you started with. Why? )