Pipes And Cisterns Q33

33.	Two pipes A and B together can fill a cistern in 4 hours. Had they been opened   separately, then B would have taken 6 hours more than A to fill the cistern. How much time will be taken by A to fill the cistern separately?
	A. 1 hour B. 2 hours C. 6 hours D. 8 hours

Answer: Option C

Explanation:

Let the cistern be filled by pipe A alone in x hours.

Then, pipe B will fill it in (x + 6) hours.

	1	+	1	=	1
	x		(x + 6)		4

	x + 6 + x	=	1
	x(x + 6)		4

 x² - 2x - 24 = 0

 (x -6)(x + 4) = 0

 x = 6.     [neglecting the negative value of x]