A - B = 3, B + C = 78, C + D = 33 and the average age of the family is 34 years Total age of the family = 4 × 34 = 136 years A + B + C + D = 136 ⇒ A + B = 136 – 33 A + B = 103 years A – B = 3 years ∴ A = 53 years B = 103 – 53 = 50 years Also C + B = 78 ⇒ C = 78 – 50 = 28 years ∴ B – C = 50 – 28 = 22 years