1.  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?
A. 3 hrs 15 min
B. 3 hrs 45 min
C. 4 hrs
D. 4 hrs 15 min

Answer: Option B

Explanation:

Part filled by the four taps in 1 hour = 4 x 1 = 2 .
6 3

Remaining part = 1 - 1 = 1 .
2 2

2 : 1 :: 1 : x
3 2

x = 1 x 1 x 3 = 3 hours i.e., 45 mins.
2 2 4

So, total time taken = 3 hrs. 45 mins.