A tap can fill a tank in 10 hours. After half the tank is filled, two more similar taps are opened. What is the total time taken to fill the tank completely?
Choose the correct answer.
A) 1 hr 20 min	B) 4 hr	C) 3 hr	D) 6 hr 40 min	E) 2 hr 50 min
Explanation:   1 tap can fill the tank in 10 hours.   Therefore   1 tap can fill half tank in 5 hours.   3 taps can fill the tank in 10/3 hour.   Therefore   3 taps can fill half tank in 10/6 hour =1 hour 40 minutes.   Total time taken=6 hour 40 minutes   Answer: Option 6 hr 40 min
<result>D</result>
A tap can fill a tank in 10 hours. After half the tank is filled, two more similar taps are opened. What is the total time taken to fill the tank completely?