A tap can fill a tank in 4 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) 3 hr
B) 1 hr 30 min
C) 2 hr 30 min
D) 2 hr
E) 4 hr
Explanation:   A tap can fill a tank in 4 hours.   Therefore the tap can fill half the tank in 2 hours.   Remaining part =1/2   After half the tank is filled, three more similar taps are opened.   Hence, total number of taps becomes 4.   Part filled by one tap in 1 hour =1/4   Part filled by four taps in 1 hour =4×14=1   i.e., 4 taps can fill remaining half in 30 minutes.   Total time taken= 2 hour + 30 minute = 2 hour 30 minutes   Answer: Option 2 hr 30 min
<result>C</result>
A tap can fill a tank in 4 hours. After half the tank is filled, three more similar taps are opened. What is the total time taken to fill the tank completely?