A takes 15 days to complete 5/7 of a work. With the help of B, they finish the whole work in 12 days. In how many days, B alone will complete the same work?
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3 i.e. 28 days.
A takes 15 days to complete a work.
A and B can complete the whole work in 12 days.
Total work = efficiency of the workers × time taken by them
A completes the work in 15 days.
So, he will complete the total work = 15 × 7/5 = 21 days
Let the efficiency of A be a
So, total work = 21 × a = 21a
A and B together complete the work in 12 days.
So, the efficiency of (A + B) = 21a/12 = 1.75a
So, the efficiency of B = 1.75a - a = 0.75a
Now, Time taken by B to complete the task alone = 21a/0.75a = 28 days