卖女孩的小火柴提问：东西两城相距多少千米？原题如下：一列客车和一列货车分别从东、西两城同时相向开出。如果两车相遇后继续前进,那么当客车行驶了全程的4/5时，货车正好行驶了全程的2/3，两车相距336千米，东、西两城相距多少千米？

数学题解答：客车行了全程的4/5，货车行了全程的2/3，两车一共行了全程的：4/5+2/3＝22/15，比全程（单位“1”）多行了：22/15-1＝7/15。这全程的7/15便是两车现在的距离336千米。所以全程就是：336÷7/15＝720（km），列出综合算式就是：336÷（4/5+2/3-1）＝720（千米）。

理解起来如有困难，请参见下图：

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