Pipe A can fill the tank 3 times faster than pipe B. If both pipes A and B running together can fill the tank in 15 minutes, then the time taken by B alone to fill the tank is:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 60 minutes
Let B alone fill the tank in t minutes. A is 3 times as fast, so A alone takes \(\frac{t}{3}\) minutes. Rates per minute add when the pipes run together:
\( \displaystyle \frac{3}{t} + \frac{1}{t} = \frac{1}{15} \)
\( \displaystyle \frac{4}{t} = \frac{1}{15} \)
\(t = 60\)
So B alone takes 60 minutes (and A alone 20 minutes).