After 20 years, he will be twice as old as his son at that time. Find their present ages. Present age of the father is = 4 x = 4 × 10 = 40 4x=4\times10=40 4x=4×10=40 years.
Let the present age of the son be x, Father's present age= 4x After 20 years , Son's age = x+20 Father's age= 4x+20 Now given that after 20 years , father will be 2twice his son's age. so, 4x+20= 2(x+20) 4x+20=2x+40 4x-2x=40-20 2x= 20 x= 20/2 x= 10 years