At Larry's Auto Supply Store, Brand X antifreeze is sold by the gallon and Brand Y motor oil is sold by the quart. Excluding sales tax, what is the total cost for 1 gallon of Brand X antifreeze and 1 quart of Brand Y motor oil?
1) Excluding sales tax, the total cost for 6 gallons of Brand X antifreeze and 10 quarts of Brand Y motor oil is $58. (There is no quantity discount)
2) Excluding sales tax, the total cost for 4 gallons of Brand X antifreeze and 12 quarts of Brand Y motor oil is $44. (There is no quantity discount.)
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cost of antifreeze
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Patrick_GMATFix
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don't worry about trying to convert gallons to quarts. just think of x as the price of one unit of antifreeze X, and think of y as the price of one unit of motor oil Y. We just want to find the value of x+y.
The full solution below is taken from the GMATFix App.
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The full solution below is taken from the GMATFix App.
-Patrick
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Hi EricKryk,
This question is built on "system math" and comes with a great shortcut, once you recognize what you're looking at.
The question asks us for the cost of 1 gallon of X and 1 quart of Y. I'm going to write that as "what is X + Y?"
Fact 1: 6X + 10Y = 58
This can be simplified to 3X + 5Y = 29. Unfortunately, there's no way to deduce what X + Y totals.
Fact 1 is INSUFFICIENT
Fact 2: 4X + 12Y = 44
This can be simplified to X + 3Y = 11. We can't figure out the value of X + Y from this either.
Fact 2 is INSUFFICIENT
Combined, we have...
3X + 5Y = 29
X + 3Y = 11
2 variables and 2 unique equations, which means we CAN solve it (and there we be just one answer), but we don't have to.
Combined, SUFFICIENT
Final Answer: C
A final note about GMAT DS questions that LOOK LIKE "system" questions; they're usually NOT system questions, so the answer is usually not C.
GMAT assassins aren't born, they're made,
Rich
This question is built on "system math" and comes with a great shortcut, once you recognize what you're looking at.
The question asks us for the cost of 1 gallon of X and 1 quart of Y. I'm going to write that as "what is X + Y?"
Fact 1: 6X + 10Y = 58
This can be simplified to 3X + 5Y = 29. Unfortunately, there's no way to deduce what X + Y totals.
Fact 1 is INSUFFICIENT
Fact 2: 4X + 12Y = 44
This can be simplified to X + 3Y = 11. We can't figure out the value of X + Y from this either.
Fact 2 is INSUFFICIENT
Combined, we have...
3X + 5Y = 29
X + 3Y = 11
2 variables and 2 unique equations, which means we CAN solve it (and there we be just one answer), but we don't have to.
Combined, SUFFICIENT
Final Answer: C
A final note about GMAT DS questions that LOOK LIKE "system" questions; they're usually NOT system questions, so the answer is usually not C.
GMAT assassins aren't born, they're made,
Rich
