A tap can fill a tank in 12 hours. After half the tank is filled, three more similar taps are opened. What is the total time taken to fill the tank completely?  Choose the correct choice from the following
A) 5 hr 30 mins	B) 7 hr 30 mins	C) 4hr 30 mins	D) 2 hr 30 mins	E) 3 hr 30 mins
Explanation:   A tap can fill a tank in 12 hours.   Therefore the tap can fill half the tank in 6 hours.   One tap take time to fill half of the tank = 6 hrs   4 taps take time to fill half of the tank = 6/4 hrs = 1 hr 30 mins   Total time taken to fill the tank = 6 hr+1 hr 30 min = 7 hr 30 mins   Answer : 7 hr 30 mins
<result>B</result>
A tap can fill a tank in 12 hours. After half the tank is filled, three more similar taps are opened. What is the total time taken to fill the tank completely?