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题库 / GMATAdvanced-PS-17
A certain manufacturer uses the function C(x)=0.04x2-8.5x+25,000 to calculate the cost, in dollars, of producing x thousand units of its product. The table above gives values of this cost function for values of x between 0 and 50 in increments of 10. For which of the following intervals is the average rate of decrease in cost less than the average rate of decrease in cost for each of the other intervals?
From x=0 to x=10
From x=10 to x=20
From x=20 to x=30
From x=30 to x=40
From x=40 to x=50
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其实想成抛物线是最简单的 根本不用计算 y=0.04x2-8.5x+25,000 这是开口向上的抛物线，对称轴在纵坐标右侧，随着X值不断增大，y值减小的速率是越来越低的，所以肯定选最后那一段
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