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.## Management Sciences

A. 6 hrs

B. 10 hrs

**C. 15 hrs**

D. 30 hrs

Explanation:

Suppose, first pipe alone takes x hours to fill the tank. Then, second and third pipes will take (x – 5) and (x – 9) hours respectively to fill the tank.

1/x + 1/(x – 5) = 1/(x – 9)

(2x – 5)(x – 9) = x(x – 5)

x2 – 18x + 45 = 0

(x- 15)(x – 3) = 0 => x = 15

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