SUM DIFFERENCE

• Did you know that addition and subtraction are related to each other? Their relationship is that they are opposites, just like night and day or hot and cold. We know that they are opposites, because addition is able to reverse, or “undo” subtraction, and subtraction is able to reverse or “undo” addition. Mathematicians have a special word for operations that are the opposite of each other like this. They call them inverse operations. Addition and subtraction are inverse operations, and multiplication and division are inverse operations.

• Because of their relationship as inverse operations, you can use subtraction to “undo” an addition problem so you can check to see if your sum (the answer to an addition problem) is correct. You can also use addition to “undo” a subtraction problem so you can check to see if your difference (the answer to a subtraction problem) is correct. Having a way to check your answer allows you to justify, or prove it. You do not have to wait to receive your scores to know whether or not you have answered the problems correctly. Checking your answer using an inverse operation, or another method of solving the problem, is an excellent habit to develop.

• There is another concern when you are solving for the sum or difference in a math problem. By the time kids are your age, they start to think they know addition and subtraction really well and sometimes do not give adding or subtracting their full attention. That is why students often make silly mistakes when they add or subtract. Remember to keep your focus on the problem you are solving, and then check your answer.

Name:__________________________________

Answer the following questions based on the reading passage. Don’t forget to go back to the passage whenever necessary to find or confirm   your answers.

1)  What is meant by the term inverseoperations?

2)   What is a sum?

3)   What is a difference?

4)   What does it mean to justify your answer?

5)  Why should you keep your attention focused on your work when you solve addition and subtraction problems?