Question

Three taps a,b and c can fill a tank in 12,15 and 20 hours respectively. if a is open all the time and b ,c are open for one hour each alternatively, the tank will be full in:

a. 1 hour
b. 3 hours
c. 6 hours
d. 7 hours
e. 8 hours

Answer 1

The tank will be full in approximately 8 hours when taps B and C alternate for one hour each.

Step-by-step explanation:

To find the time it takes to fill the tank, we need to find the combined rate at which taps B and C are filling the tank when they alternate for one hour each.

Tank capacity: 1 (since tapping A is open all the time)
Tank filling rate by tap A: 1/12
Tank filling rate by tap B: 1/15
Tank filling rate by tap C: 1/20
Tank filling rate by taps B and C when alternating: (1/15) + (1/20) = 7/60

Hence, the tank will be full in 60/7 hours, which is approximately 8.57 hours. Therefore, the correct answer is 8 hours, option (e).