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?

Answer: Option B

Solution

Answer: Option B

Solution:

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

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