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标题: Old topic, travel distance[:)] [打印本页]

作者: ob 时间: 2004-12-15 03:09
标题: Old topic, travel distance[:)]

轮胎放在后轮能使用3000米，放在前轮能使用5000米，现将前后轮换新，行驶到一定距离后前后轮互换，最多能行驶多少米？在什么时侯换？

作者: tcpip004 时间: 2004-12-15 11:47
标题: 回复：Old topic, travel distance[:)]

1875

作者: achen 时间: 2004-12-15 18:59
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作者: sean9991 时间: 2004-12-15 19:58
标题: tcpip004 is correct

It's a linear programming problem.

Maximize: x + y

Subject to: x/3000 + y/5000 <= 1; x/5000 + y/3000 <= 1.

The optimal solution is x = y = 1875.

So 3750 is the total milage the tires can last.

BTW, I think the unit should be miles instead of meters. Nobody will purchase a tire that lasts only several kilometers :-).

作者: achen 时间: 2004-12-15 21:54
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作者: sean9991 时间: 2004-12-15 23:21
标题: 回复：回复what is wrong with this solution??

There is a confusion in your formular.

If Y is the total distance the car travelled, then Y = X + 3000(1-X/5000). And Why do you want to minimize it? We should maximize Y instead.

作者: achen 时间: 2004-12-16 00:53
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作者: achen 时间: 2004-12-16 01:17
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