A is twice as efficient as B, and they take equal time as the time taken by C and D to do this work together. If C and D can complete the same work in 15 and 20 days respectively, then. In how many days can A alone complete the work?

Solution (By Examveda Team)

A = 2B
B = $$\frac{{\text{A}}}{2}$$

Efficiency of (A + B) = Efficiency of (C + D)
$$\eqalign{ & {\text{A}} + {\text{B}} = 7 \cr & \Rightarrow {\text{A}} + \frac{{\text{A}}}{2} = 7 \cr & \Rightarrow {\text{A}} = \frac{{14}}{3} \cr & {\text{Time of A}} = \frac{{60 \times 3}}{{14}} = \frac{{90}}{7}{\text{Answer}} \cr} $$