Having the same capacity 9 taps fill up a water tank in 20 minutes. How many taps of the same capacity required to fill up the same water tank in 15 minutes?
Answer: (2) 12
T1N1 = T2N2
Where, T = time and N = number of taps
Then, T1 = 20 minutes, N1 = 9, T2 = 15 minutes and N2 = ?
9 x 20 = 15 x N2
N2 = 9 x 20/15
N2 = 12
Hence, the answer (2) 12.