A and B working together can do a work in 10 days. If A can do the work in 15 days, then how many days will B take to do the same work?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 30
A person who finishes a job in \(n\) days does \(\frac{1}{n}\) of it in one day, and the one-day work of people working together is added. So B’s one-day work is the joint one-day work minus A’s.
A and B together: \(\frac{1}{10}\) of the work a day
A alone: \(\frac{1}{15}\) of the work a day
B alone: \(\displaystyle \frac{1}{10}-\frac{1}{15}=\frac{3-2}{30}=\frac{1}{30}\) of the work a day, so B takes 30 days