If p : q : r = 1 : 2 : 4, then 5p^2 + q^2 + r^2 is equal to =

Answer: Option C

$$\begin{array}{rl}& \text{p}:\text{q}:\text{r}\\ & 1:2:4\\ & x:2x:4x\\ & \therefore \sqrt{5p^2+q^2+r^2}\\ & =\sqrt{5x^2+4x^2+16x^2}\\ & =\sqrt{25x^2}\\ & =5x\\ & =5p\end{array}$$