Having the same capacity 9 taps fill up a water tank in 20 minutes. How many taps of the same capacity are required to fill up the same water tank in 15 minutes?

12

9 taps → 20 min

Total work = no. of pipes × total time

                = 9 × 20 = 180

In 15 minutes → no. × 15 = 180

                                   h = \(\frac{180}{15}\) = 12

No. of taps = 12