Question

Two taps A and B can fill a cistern in 10 and 15 minutes respectively. Both
the taps are opened together but at the end of 3 minutes, tap is turned
off. In how much time will the cistern be filled?

Answer 1

A and B can fill the cistern in 10 min and 15 min respectively .

Part of cistern filled by A in 1 minute = 1/10

Part of cistern filled by B in 1 minute = 1/15

Let them operate together for n minutes , After which A is turned off

Amount filed by A and B together = n [(1/10) + (1/15)] = 3n/20

Remaining part of the cistern is filled by B in 5 min

Amount filled by B in 5 min = 5(1/15) = 1/3

Total amount to be filled = 1

(3n/20) + (1/3) = 1

9n + 20 = 60

n = 40/9

= 4.44 minutes

Hope it will help you .