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 the tank = 3hrs.
Part filled by the four taps in 1 hour = (4×1/6)
= 2/3.
Remaining part = (1 - 1/2)
= 1/2.
Therefore, 2/3 : 1/2 :: 1 : x
=> x = (1/2×1×3/2)
=> x = 3/ 4 hrs i.e 45 mins.
So, total time taken = 3 hrs 45 min.