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6.	Three pipes A, B and C can fill a tank from empty to full in 30 minutes, 20 minutes and 10 minutes respectively. When the tank is empty, all the three pipes are opened. A, B and C discharge chemical solutions P, Q and R respectively. What is the proportion of solution R in the liquid in the tank after 3 minutes ?
	A.  5/11
	B.  6/11
	C.  7/11
	D.  8/11

Solution

Part filled by (A + B + C) in 3 minutes = 3(1/30+1/20+1/10) = (3×11/60) = 11/20. Part filled by C in 3 minutes = 3/10. Required ratio = (3/10×20/11) = 6/11.

7.	Two taps A and B can fill a tank in 5 hours and 20 hours respectively. If both the taps are open then due to a leakage, it took 30 minutes more to fill the tank. If the tank is full, how long will it take for the leakage alone to empty the tank?
	A.  8 hrs
	B.  9 hrs
	C.  18 hrs
	D.  36 hrs

Solution

Part filled by (A + B) in 1 hour = (1/5 + 1/20) = 1/4. So, A and B together can fill the tank in 4 hours. Work done by the leak in 1 hour = (1/4 - 2/9) = 1 / 36. Therefore, Leak will empty the tank in 36 hrs.

8.	Two pipes A and B can fill a tank in 20 and 30 minutes respectively. If both the pipes are used together, then how long will it take to fill the tank ?
	A.  12 min
	B.  15 min
	C.  25 min
	D.  50 min

Solution

Part filled by A in 1 min = 1/20. Part filled by B in 1 min = 1/30. Part filled by (A+B) in 1 min = (1/20 + 1/30) = 1/12. Both the pipes can fill the tank in 12 minutes.

9.	Pipes A and B can fill a tank in 5 and 6 hours respectively. Pipe C can empty it in 12 hours. If all the three pipes are opened together, then the tank will be filled in
	A.  1×13/17 hours
	B.  2×8/11 hours
	C.  3×9/17 hours
	D.  4×1/2 hours

Solution

Net part filled in 1 hour = (1/5 + 1/6 -1/12) = 17/60. Therefore, the tank will be full in 60/17 hrs. ‹=› 3×9/17 hrs.

10.	12 buckets of water fill a tank when the capacity of each tank is 13.5 litres. How many buckets will be needed to fill the same tank, if the capacity of each bucket is 9 litres?
	A.  8
	B.  15
	C.  16
	D.  18

Solution

Capacity of the tank = (12×13.5) litres = 162 litres. Capacity of each bucket = 9 litres. Number of buckets needed = (162/9) ‹=› 18.