We've already learned a lot about subtraction number families. When dealing with comparison word problems, writing them in number families can help you solve them. How do we write a number family for word problems? We write a number family for word problems using variables (letters).
Think about this word problem: Mary has more balloons than Tim. We will use the first letters of the two names in our number family. In this case, we will use the variables M for Mary and T for Tim.
Think back to what you know about word families. Where do we put the greatest (larger) number? The greatest number is always put at the end of the arrow. Our word problem says that Mary has more balloons than Tim. Since Mary has more, Mary equals the greatest number. Only the lesser (smaller) numbers are left. Tim equals the lesser number.
We write our number family using the letters M and T like this:
What about this comparison word problem? Pam has fewer crayons than Seth. Which are our greatest and lesser numbers here? Correct-since Pam has fewer crayons than Seth, Pam equals the lesser number, while Seth equals the greatest number. Again, we use the first letters of the two names. We will use P for Pam and S for Seth. We write our number family for this comparison word problem this way:
