一艘轮船所带的燃料最多可用12小时，驶出时顺水，每时行驶30千米，返回时逆水，每时行的路程是顺水的4/5。这艘轮船最多驶出多远就应返回？（用多种方法解答）

数学题解答：先用方程解：设行出x小时后就应返回。

数量关系：行出的路程＝返回的路程

方程：30x=(12-x)×24

解得：x=5又1/3

5又1/3　×　30　＝　160（千米）

答：这艘轮船最多驶出160千米就应返回。

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