The average of ten numbers is 7. If each number is multiplied by 12, then the average of the new set of numbers is :

Answer: Option D

Average of 10 numbers = 7
Sum of these 10 numbers = (10 × 7) = 70
$$\begin{array}{rl}& \therefore x_1+x_2+.....+x_{10}=70\\ & \Rightarrow 12x_1+12x_2+.....+12x_{10}=840\\ & \Rightarrow \frac{12x_1+12x_2+.....+12x_{10}}{10}=84\end{array}$$
⇒ Average of new numbers is 84