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 :
n² = a x b, where ‘a’ and ‘b’ are the extra time taken if both work individually than if both work together.
Therefore, n² = 9 x 6.25
=> n = 3 x 2.5 = 7.5

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