arithmetic - a tap can fill a tank in 6 hours after half the tank is filled three more similar taps are opened what is the total time taken to fill the tank completely - skillgun

Time taken by one tap to fill half of the tank = 3 hrs.
Part filled by the four taps in 1 hour = 4 x 1/6 = 2/3 .
Remaining part = 1 - 1/2 = 1/2 .
=> 2/3 : 1/2 :: 1 : x
=> x = 1/2 x 1 x 3/2 = 3/4 hours
i.e., 45 mins.
So, total time taken = 3 hrs. 45 mins.