Q. 554.6( 9 Votes )

Two pipes running together can fill a cistern in   minutes. If one pipe takes 3 minutes more than the other to fill it, find the time in which each pipe would fill the cistern.

Answer :

Let one pipe fills a cistern in x mins.

Other pipe fills the cistern in (x + 3) mins.


Running together can fill a cistern in minutes = 40/13 mins


Part filled by one pipe in 1min =


Part filled by other pipe in 1min =


Part filled by both pipes Running together in 1min =





13x2 + 39x = 80x + 120


13x2 – 41x – 120 = 0


Using the splitting middle term – the middle term of the general equation is divided in two such values that:


Product = a.c


For the given equation a = 13 b = – 41 c = – 120


= 13. 120 = – 1560


And either of their sum or difference = b


= – 41


Thus the two terms are – 65 and 24


Difference = – 65 + 24 = – 41


Product = – 65.24 = – 1560


13x2 – 65x + 24x – 120 = 0


13x(x – 5) + 24(x – 5) = 0


(x – 5) (13x + 24) = 0


(x – 5) = 0 (13x + 24) = 0


x = 5 or x = – 24/13


x = 5 (speed cannot be negative fraction)


Hence one pipe fills a cistern in 5 minutes and other pipe fills the cistern in (5 + 3) = 8 minutes.


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