A father is 60 years old and his son is half his age. How old was the boy when his father was four times his age? 6 years old 7 years old 8 years old 9 years old 10 years old

The father is 60, and the son is half of 60, so the son is 30.

The difference in ages is 60 - 30 = 30.

The difference in ages is 30 years. That difference is always true, no matter how old they are.

When the father was 4 times the age of the son, the son was b years old and the father was 4b years old. The difference in ages is still 30, so that gives us our equation.

4b - b = 30

3b = 30

b = 10

Answer: 10 years old