If the operating costs of a delivery truck are 16+(x/2) cents per mile when the truck travels x mi/hr and the driver earns $10 per hour, what is the most economical speed, to the nearest integer, to operate the truck on a 200-mile-long road, where the minimum speed is 50 mi/hr and the maximum speed is 75 mi/hr ? (A)50 (B)56 (C)63 (D)75 我的算式是 10．(200/x) - 200．[16+(x/2)]．(1/100)，50<=x<=75 然後再去算极值 但好像怪怪的 找不出答案 不晓得算式是否有问题 先谢谢热心回答的版友 --

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