In a bag, there are coins of 25 p, 10 p and 5 p in the ratio of 1 : 2 : 3. If there is Rs. 30 in all, how many 5 p coins are there?

Answer: Option C

Let the number of 25 p, 10 p and 5 p coins be x, 2x, 3x respectively
Then, sum of their values
$$\begin{array}{rl}& =Rs.\left(\frac{25x}{100}+\frac{10\times 2x}{100}+\frac{5\times 3x}{100}\right)\\ & =Rs.\frac{60x}{100}\\ & \therefore \frac{60x}{100}=30\iff x=\frac{30\times 100}{60}=50\\ & \text{Hence,}\text{the}\text{number}\text{of}\text{5p}\text{coins}\\ & =\left(3\times 50\right)\\ & =150\end{array}$$