Question

There are 7 members in a family which includes two grandparents, two parents, and three siblings. Father’s age is 45 years and Mother’s age is 42. Average age of two siblings is 15 whereas the third sibling’s age is 4 years more than the average age of the three siblings. If the average age of family is 40 years then find average age of grandparents.

1. 63 years
2. 67 years
3. 71 years
4. 75 years

Answer 1

Correct Answer - Option 3 : 71 years

Given:

Father’s age = 45

Mother’s age = 42

Average age of two sibling = 15

Age of third sibling = 4 + Average age of all three siblings

Average age of family = 40

Formula used:

Average age = Sum of ages of all persons/ Number of persons

Calculations:

Let the average age of three siblings be ‘x’ and the average age of grandparents be ‘g’.

Age of third sibling = x + 4

Sum of age of two siblings = 15 × 2 = 30

⇒ [30 + (x +4)]/3 = x

⇒ 30 + x + 4 = 3x

⇒ 2x = 34

⇒ x = 17

Total age of siblings = 3x = 51

Average age of family = 40 = (45 + 42 + 51 + 2g)/7

⇒ 138 + 2g = 280

⇒ 2g = 142

⇒ g = 71

∴ The average age of grandparents is 71 years