A man does double the work done by a boy in the same time. The number of days that 3 men and 4 boys will take to finish a work which can be done by 10 men in 8 days is ?

$$\eqalign{ & \frac{{\text{M}}}{{\text{B}}} = \frac{2}{1}\left( {{\text{Efficiency}}} \right) \cr & {\text{Now,given}} \cr & \left( {{\text{3M}} + {\text{4B}}} \right) \times {\text{D}} = 10 \times 2 \times 8 \cr & \left( {{\text{3}} \times 2 + 4 \times 1} \right) \times {\text{D}} = 10 \times 2 \times 8 \cr & 10 \times {\text{D}} = 10 \times 16 \cr & {\text{D}} = 16{\text{ days}} \cr} $$