tailieunhanh - Master gmat 2010 part 29

The correct answer is (D). In the weighted-average formula, 315 annual gallons receives a weight of 4, while the average annual number of gallons for the next six years (x) receives a weight of 6: 378 5 1260 1 6x 10 3780 5 1260 1 6x 3780 2 1260 5 6x 2520 5 6x 420 5 x This solution (420) is the average number of gallons needed per year, on average, during the next 6 years. To guard against calculation errors, check your answer by sizing up the question. Generally, how great a number are you looking for? Notice that.

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