数学题：姐姐比妹妹大5岁，姐姐8年后的年龄是妹妹3年前的5倍。姐姐和妹妹今年多少岁？

数学题解答：题目中有两个未知数，用方程会容易些。

解：设妹妹今年x岁，则姐姐岁数可以用（x+5）表示。

根据“姐姐8年后的年龄是妹妹3年前的5倍”来列出方程。

x+5+8=(x-3)×5

x+13=5x-15(根据等式性质，两边同时减去x，得)

4x-15=13

x=7

x+5=7+5=12

答：姐姐和妹妹今年分别是12岁、7岁。

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