A works three times as fast as B. If B alone can complete a piece of work in 18 days, in how many days can A and B together finish the work?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \(4\frac{1}{2}\) days
Working three times as fast means doing the same work in one-third of the time.
A alone takes \(\displaystyle \frac{18}{3}=6\) days
One-day work of A and B \(\displaystyle =\frac{1}{6}+\frac{1}{18}=\frac{3+1}{18}=\frac{2}{9}\)
Time together \(\displaystyle =\frac{9}{2}=4\frac{1}{2}\) days
Together they finish the work in \(4\frac{1}{2}\) days.