Correct Answer - Option 3 : 40 years
Given:
Average age = 40 years
Formula used:
Average = Sum of all the terms/Total number of terms
Calculation:
A ∶ B = 3 ∶ 4
And, B ∶ C = 4 ∶ 5
Then, A ∶ B ∶ C = 3 ∶ 4 ∶ 5
Let the age of A, B and C be 3x, 4x and 5x
Sum of ages of all the persons = 3x + 4x + 5x = 12x
Average = 12x/3 = 4x
⇒ 4x = 40
⇒ x = 10
∴ The age of B is 40