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

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