Two pipes A and B can fill a tank in 6 hours and 9 hours respectively. They are opened alternately for 1 hour each starting with pipe A first. In how many hours the tank will be filled?

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Two pipes A and B can fill a tank in 6 hours and 9 hours respectively. They are opened alternately for 1 hour each starting with pipe A first. In how many hours the tank will be filled?

A5

B4

C6

D7

Answer:

D. 7

Read Explanation:

Capacity of the tank = LCM of the time taken by A and B. Capacity of the tank = 18 A’s efficiency = 18/6 = 3 B’s efficiency = 18/9 = 2 2 hours work for A and B = (3 + 2) = 5 6 hours = 15 units 7 hours = 18 units. (At last A fills remaining 3 units) Tank will be filled in 7 hours.

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