Question

Ten years ago father was 4times the age of son. Ten year hence father is twice the age of son. find the age of father

Answer 1

let the fathers age be x and son's age be y

before 10 years 
x+10=4(y+10)
x-10=4y-40
4y-x=3               ....... eq1

After 10 years
x+10=2(y+10)
x+10=2y+20
x-2y=10            ............eq2

add eq 1 and 2
4y-x+x-2y=10+30
2y=40
y=20
Put value of y in eq 1
4(20)-x=30
80-x=30
80-30=x
x=50 

Hence fathers age is 50 and sons age is 20