You've learned about classification word problems and comparison word problems. You've also learned about difference word problems. Since we've learned how to make number families from the information in word problems, let's now try t­o solve them.

Take a look at this problem:

Athena collected 15 pens. Lee collected 20 more pens than Athena. How many pens did Lee collect?

We need to make a number family that shows the difference. Lee has collected more pens, so he's the greatest number (larger number). Athena is a lesser number (smaller number).

The difference is the other lesser number. How do we solve for Lee's pens? Do we add or subtract? We need to add: 20 plus 15 equals 35 (20 + 15 = 35). Lee collected 35 pens.

Let's try another problem. This time, it tells us what happens first and what happens next.

Tory has books. Her mom gave her 7 more books. She now has 28 books. How many books did she start with?

For this kind of problem, you have to put the values forward along the arrow if you get more. Put them backward if you get less. Did Tory get more or less? She got more. So we put the values forward.

How many books did Tory have before? Subtract 28 minus 7, an­d it equals 14. Tory had 14 books to start.

There are problems that don't tell us if there are more or less, or if something came first or next.

There are 16 red apples in a basket, and the rest are green. If there are 27 apples, how many are green?

Remember how we made the number family.

How many apples are green? Subtract 27 minus 16, and it equals 11. There are 11 green apples.