Two pipes can fill a cistern in 8 hours and 12 hours respectively

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Exercise :: Pipes and Cistern - General Questions

Two pipes can fill a tank in 20 and 24 minutes respectively and a waste pipe can empty 3 gallons per minute. All the three pipes working together can fill the tank in 15 minutes. The capacity of the tank is:

A.	60 gallons
B.	100 gallons
C.	120 gallons
D.	180 gallons

Answer: Option C

Explanation:

Work done by the waste pipe in 1 minute =	1	-		1	+	1
15	20	24

=		1	-	11
15	120

= -	1	. [-ve sign means emptying]
40

Volume of	1	part = 3 gallons.
40

Volume of whole = (3 x 40) gallons = 120 gallons.

A tank is filled in 5 hours by three pipes A, B and C. The pipe C is twice as fast as B and B is twice as fast as A. How much time will pipe A alone take to fill the tank?

A.	20 hours
B.	25 hours
C.	35 hours
D.	Cannot be determined
E.	None of these

Answer: Option C

Explanation:

Suppose pipe A alone takes x hours to fill the tank.

Then, pipes B and C will take	x	and	x	hours respectively to fill the tank.
2	4

	1	+	2	+	4	=	1
x	x	x	5

	7	=	1
x	5

x = 35 hrs.

Page 2

Exercise :: Pipes and Cistern - General Questions

11.

One pipe can fill a tank three times as fast as another pipe. If together the two pipes can fill the tank in 36 minutes, then the slower pipe alone will be able to fill the tank in:

A.	81 min.
B.	108 min.
C.	144 min.
D.	192 min.

Answer: Option C

Explanation:

Let the slower pipe alone fill the tank in x minutes.

Then, faster pipe will fill it in	x	minutes.
3

	1	+	3	=	1
x	x	36

	4	=	1
x	36

x = 144 min.

12.

A large tanker can be filled by two pipes A and B in 60 minutes and 40 minutes respectively. How many minutes will it take to fill the tanker from empty state if B is used for half the time and A and B fill it together for the other half?