### Of the three numbers, the first is twice the second and the second is twice the third. The average of the reciprocal of the numbers is $\frac{7}{72}$ . The numbers are:

A. 16, 8, 4

B. 20, 10, 5

C. 24, 12, 6

D. 36, 18, 9

$\begin{array}{l}\text{Let the number be x.}\\ \text{Then, second number = 2x.}\\ \text{First number = 4x}\\ \therefore\frac{1}{x}+\frac{1}{2x}+\frac{1}{4x}=\frac{7}{72}\times3\\ \Rightarrow\frac{7}{4x}=\frac{7}{24}\\ \Rightarrow4x=24\\ \Rightarrow x=6\end{array}$ So, the number are 24, 12 and 6