A and B together can do a piece of work in 15 days, whereas B alone can do the same work in 20 days. In how many days can A alone do the work?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 60
Work done in one day adds up when people work together, so A's one-day work = (A and B's one-day work) − (B's one-day work).
A and B together in one day: \(\frac{1}{15}\) of the work
B alone in one day: \(\frac{1}{20}\) of the work
A alone in one day: \(\displaystyle\frac{1}{15}-\frac{1}{20}=\frac{4-3}{60}=\frac{1}{60}\)
So A alone needs 60 days