Question

A man is 3 times his son's age.10 years hence man will be 2 times the age of his son. What was the age of man when his son was 20 years? Select one:

Answer 1

Son's age = a

man's age = 3a

After 10years

son's age = a + 10

Man's age = 3a + 10   or    2(a+10)

3a + 10 = 2a + 20

a = 10

Son's age  = 10

Father's age = 30

When Son's age 20 years Father's age will be 30+10 = 40years

Answer 2

Let the son's age be x.
Therefore, the man's age = 3x
After 10 years,
Son's age = x+10
Man's age = 3x+10
Given that after 10 years,the man will be 2 times the age of his son
3x+10 = 2(x+10)
3x+10 = 2x+20
3x-2x = 20-10
x = 10.
Therefore present age of son is x and man is 3x = 3(10) = 30 years.
Son's age after ten years = x+10 = 10+10 = 20 years
At that time man's age = 2x+20 =2(10)+20 = 20+20 =40 years.
Therefore when son was 20 years his age will be 40 years.

Hope it helps you....