(b) Let the present age of father be 3xand daughter be x So, 4 yr ago, father's age and daughter's age was (3x - 4) and (x - 4) respectively. Therefore,
3x−4
x−4
=
4
1
3x - 4 = 4x - 16 ⇒ x = 12 yr ∴ Daughter’s present age, x = 12 yr and father's present age, 3x = 3 x 12 = 36 yr ∴ Present average age =