# QA – Placement Quizzes | Pipes and Cisterns | Question 5

Working alone, two pipes A and B require 9 hours and 6.25 hours more respectively to fill a pool than if they were working together. Find the total time taken to fill the pool if both were working together.**(A)** 6**(B)** 6.5**(C)** 7**(D)** 7.5**Answer:** **(D)****Explanation:** Let the time taken if both were working together be ‘n’ hours.

=> Time taken by A = n + 9

=> Time taken by B = n + 6.25

In such kind of problems, we apply the formula :

n^{2} = a x b, where ‘a’ and ‘b’ are the extra time taken if both work individually than if both work together.

Therefore, n^{2} = 9 x 6.25

=> n = 3 x 2.5 = 7.5

Thus, working together, pipes A and B require 7.5 hours.

Quiz of this Question

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