GMAT question - Water pipes A and B can fill a tank in 5 and 7 hours...

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Type: Problem Solving

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Water pipes A and B can fill a tank in 5 and 7 hours respectively if used on their own. If both pipes are used at the same time, how long will it take to fill the tank?

2 hours 11 minutes
2 hours 55 minutes
3 hours
3 hours 5 minutes
12 hours