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This problem trains for: SAT-I, AMC-8, GMAT.

A swimming pool must be refilled with 18150 gallons of water. For this, water is poured from three cisterns. The output of the first hose is double as large as that of the second hose, while the output of the third hose is one third of the output of the first hose. If the pool was refilled in five and a half hours, what was the output of the third hose in gallons per minute?

Denote the output of the third hose with x, then the output of the first hose will be 3x and the output of the second hose will be 3x/2:

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