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1. A family consists of grandparents, parents and three grandchildren. The average age of the grandparents is 67 years that of the parents is 35 years and that of the grandchildren is 6 years. What is the average age of the family?

A. $28 \frac{4}{7} years$

B. $31 \frac{5}{7} years$

C. $32 \frac{1}{7} years$

D. None of these

Solution:

Required average

\begin{aligned} = \frac{67 \times 2 + 35 \times 2 + 6 \times 3}{2 + 2 + 3} \\ = \frac{134 + 70 + 18}{7} \\ = \frac{222}{7} \\ = 31 \frac{5}{7} years \end{aligned}

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