Kamal can do a work in 15 days. Bimal is 50% more efficient then Kamal. The number of days, Bimal will take to do the same piece of work, is = ?

Answer: Option B

Ratio of times taken by Kamal and Bimal
$$\begin{array}{rl}& =150:100\\ & =3:2\end{array}$$
Suppose Bimal takes x days to do the work
$$\begin{array}{rl}& \Rightarrow 3:2::15:x\\ & \Rightarrow x=\left(\frac{2\times 15}{3}\right)\\ & \Rightarrow x=10\text{ days}\text{.}\end{array}$$