小华看一本240页的故事书,看了三天后,看了的页数正好比剩下页数的2倍多15页,小华

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  • 设看完X,剩下Y,可得方程组:

    X+Y=240···················A

    X-2Y=15····················B

    A式-B式得 3Y=225,Y=75,则X=165

    算出看完了165页,剩下75页