CHAPTER 3: DOES IT ADD UP?Actually, figuring missing addends is a good exercise to use to begin to learn to subtract. Here how it works. Find the missing addend in the following equation: 7 + ____ = 15 You can solve this problem by trying different numbers until one works. This method is called guess and check because you try a number and check to see if it works. If it doesn work, then you try another number using what you have learned from the previous guess. Look up this method in Chapter 12. You can also use subtraction to help you here. Since 15 is the larger number, you can subtract 7 from it so it looks like this: 15 �7 = 8 Now let go back to the first problem and try 8 as the missing addend. 7 + 8 = 15 It works because addition and subtraction are friendly to each other in a special way. Check this out in Chapter 4.WAYS TO ADDThere are several ways to add numbers together. As you get older you will find that the way you most often use is by mental math. We talked about that earlier in this chapter.38