arithmetic - three taps a b and c can fill a tank in 24 30 and 40 hours respectively if a is open all the time and b and c are open for one hour each alternately the tank will be full in - skillgun

Solution: (A+B)'s 1 hour's work = (1/24 + 1/30) = 9/120 = 3/40.
(A+C)'s 1 hour's work = (1/24 + 1/40) = 8/120 = 2/30.
Part filled in 2 hours = (3/40 + 2/30) = 17/120.
Part filled in 12 hours = (6 * 17/120) = 17/20.
Remaining part = (1 - 17/20) = 3/20.
now, it is the time of A and B and 3/20 part is filled by A and B in 1 hour, then, 3/40 part will filled in 2 hours.
.'. total time taken to fill the tank = (12 + 2) = 14 hours