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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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难道不是用每段的差除以10就可以算出rate了吗。。。？
到底是除以10还是除以原来的值啊？应该不会那么笨考计算吧？但说decrease rate又感觉应该是除原来的值
我的意思就是除以原来的值，抛物线想，在抛物线的对称轴左侧的部分，随着x值的增大，抛物线上每个点的斜率的绝对值是减小的，所以就是decrease rate不断降低。我是这样理解的
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