Pipe P can fill a tank 8 hours and Pipe Q can fill it in 10 hours. If

Pipe P can fill a tank 8 hours and Pipe Q can fill it in 10 hours. If they are opened an alternate hour and if pipe P is opened first, then in how many hours the tank should be full?1. 8.8 hours2. 6.3 hours3. 7.5 hours4. 3.6 hours

Answer» Correct Answer - Option 1 : 8.8 hours

Given:

Pipe P can fill the tank = 8 hours

Pipe Q can fill the tank = 10 hours

Concept used:

Total capacity = LCM

Efficiency of inlet tap always positive and efficiency of outlet tap is always negative

Formula used:

Efficiency = Total capacity/Time

Calculation

Total capacity = LCM = 40

First hours P comes fill tank = 5

Second Q comes fill the tank = 4

Tank fill in 2 hours = 5 + 4 = 9

Tank fill in 8 hours = 9 × 4 = 36

Remaining = 40 – 36 = 4

Now, P comes and fill the remaining part of the tank = 4/5 = 0.8 hours

Total time = 8 + 0.8 = 8.8 hours

∴ Total time taken by pipes to fill the tank alternately is 8.8 hours