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:

60 minutes

The correct answer is Option (3) → 60 minutes

Let the time taken by pipe B alone to fill the tank = t minutes

Then, time taken by pipe A alone = t / 3 minutes

Rate of A = 1 / (t/3) = 3/t

Rate of B = 1 / t

Both together fill the tank in 15 minutes → combined rate = 1 / 15

Combined rate = Rate of A + Rate of B:

$\frac{3}{t} + \frac{1}{t} = \frac{1}{15}$

$\frac{4}{t} = \frac{1}{15}$

$t = 4 × 15 = 60$ minutes

Therefore, pipe B alone will take 60 minutes to fill the tank