数学题：A×B×C＝300，A×C＝100，A×4＝C，求A、B、C各是多少？

数学题解答：把题中给出的三个等式分别编上序号，如下：

①A×B×C＝300，②A×C＝100，③A×4＝C

由①A×B×C＝300，②A×C＝100可知：B＝300÷100＝3。

又由②A×C＝100，③A×4＝C可知：A×A×4＝100

即A×A=25，所以A＝5

那么C＝5×4=20。

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