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 = ?

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