Two pipes A and B can fill a tank in 18 and 6 h, respectively.

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Two pipes A and B can fill a tank in 18 and 6 h, respectively. If both the pipes are opened simultaneously, how much time will be taken to fill the tank ?

1. 4¹/₂h
2. 7 h
3. 6 h
4. 10 h

Correct Option: A

Part filled by A in 1 h = 1/18
Part filled by B in by 1 h = 1/6
Part filled (A + B) in 1 h =1/18 + 1/6 = (1 + 3)/18 = 4/18 = 2/9
Hence, both the pipes together will fill the tank in 9/2 h or 4¹/₂ h