A and B can do a job in 10 days and 5 days respectively. They worked together for two days, after which B was replaced by C and the work was finished in the next three days. How long will C alone take to finish 40% of the job?

Answer: Option D

Solution

Answer: Option D

Solution:

Two days work of A and B = 3 × 2 = 6
Remaining work = 10 - 6 = 4
Now as per question
$$\begin{array}{rl}& \frac{4}{1+\text{C}}=3\\ & \frac{4}{3}=1+\text{C}\\ & \text{C}=\frac{1}{3}\end{array}$$
So that 40% of total work done by $$\text{C}=\frac{10\times 40\%}{\frac{1}{3}}=12$$