Hi Mo2men,
We're told that 3 pumps each pump water at a constant rate. We're asked how long it would take to fill up a 30,000 gallon tank.
If we're meant to assume that the tank starts off 'empty', then this is a relatively straight-forward prompt (we need the rates of the 3 pumps to answer the question).
1) Hoses X and Z each pump water at constant rate of 120 gallons per hour.
This Fact tells us nothing about the rate of Hose Y, so the answer will vary depending on that rate.
Fact 1 is INSUFFICIENT
2) Hose Y pumps water at half the rate of X.
This Fact tells us nothing about any of the rates, so the answer will vary depending on those rates.
Fact 2 is INSUFFICIENT
Combined, we know....
Hose X = 120 gallons/hour
Hose Z = 120 gallons/hour
Hose Y = 60 gallons/hour
We can now calculate how long it would take to pump 30,000 gallons of water. Again, if we're meant to assume that the tank starts off empty, then this information is SUFFICIENT. IF there's some water in the tank though, then the information is INSUFFICIENT (we would need to know the exact volume of water that needs to be pumped).
Final Answer: C
GMAT assassins aren't born, they're made,
Rich
