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.