math
posted by Beth .
First of all I don't just need the answer I need it explained where a third grader can understand it. I actually know the answer, but I don't know how to explain it to a third grader. ?Doug has 170 stamps in his collection. His first book of stamps has 30 more stamps in it than his second book. How many stamps are in each book? Thanks

Suppose there are P stamps in Doug's first book. Then there are (P+30) stamps in his second book. The total number of stamps in his collection is 170, and his collection equals the number of stamps in the first book plus the number in the second book. So P + (P+30) = 170, which means that 2xP + 30 = 170, so 2xP = 17030 = 140. If 2xP = 140, then P = 140/2 = 70. This is the number in his first book, so he's got 70+30=100 stamps in his second book. Check the answer: 70+100=170, and 100 is 30 more than 70. Correct!