Question

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

Answer 1

f=60, s=60/2=30

(60-x)/(30-x)=4

60-x=120-4x

60+3x=120

3x=60

x=20  

s=30-x

s=30-20

s=10

So the boy was 10 years old when his father was four times his age.