Question 998990
let son's age be x
then father's age = 2x

20 years ago their ages

son (x-20)
father ---- (2x-20)

According to the information

(2x-20)=4(x-20)

2x-20 = 4x-80

2x=60

/2
x=30

Son's age = 30

Father's age = 30*2 = 60