Solving an age problem with basic math

by casi
(pueblo)

Janet and younger brother Jared are 5 years apart. The sum of their ages is 13. How old is each?

Solution by Trial and error

13 = 12 + 1 The difference is 11

13 = 11 + 2 The difference is 9

13 = 10 + 3 The difference is 7

13 = 9 + 4 The difference is 5

So they must be 9 and 4 years old.

Since Jared is the younger brother, he is 4.

Then, Janet is 9.