RRB Group-D Model Paper 14 with answers for online practice

Let the age of the grandchild be x
⇒ Age of the mother = 2x
⇒ Age of the grandfather = 3 × (2x) = 6x
⇒ Average = Sum of three ages/3
⇒ 51 = (x + 2x + 6x)/3
⇒ 51 = 9x/3
⇒ x = 17
⇒ Age of grandfather = 6x = 102 years
⇒ Age of grandchild = x = 17 years
∴ Required difference = 102 – 17 = 85