Question

A father is 60 yrs old son is half his age .How old was the boy when his father was four times his age

Answer 1

let f be the fathers age and let s be the sons age

f = 60 s = 30
when f = 45
s = 15 which is only a third if his fathers age

when f = 40
s = 10 which is a quarter of his fathers age

therefore when his father was 4 times his age, the son was 10

Answer 2

Let F be the father's age, let S be the son's age
when: F = 60,
S = F/2 = 60/2 = 30

this means S = F-30

this means:
F/4 = F -30
F = 4F - 120
-3F = -120
F = 40

If the boy was 4 times less his father's age,
at this instance:
S = 40/4 = 10

therefore the son was 10 years old, the father was 40