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?
Options:
A) 3hr
B) 3hr 45min
C) 4hr 15min
D) 2hr 1min
E) 1hr 45min
Time taken by one tap to fill the half tank = 3 hr   part filled by the 4 taps in 1hour = 4*1/6 = 2/3   Remaining part = 1-1/2 = 1/2   2/3:1/2::1:x   x = 3/4hr = 45min   Total time taken = 3hr 45min   Answer is 3hr 45min
<result>B</result>
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?