问题标题:
XiaoHongreadastorybookforthreedays.Onthefirstday,heread25pages.Onthesecondday,heread2/5ofthebook.onthethirdday,heread9/20ofthebook.thenthereare()pagesinthebook.
问题描述:

XiaoHongreadastorybookforthreedays.Onthefirstday,heread25pages.Onthesecondday,he

read2/5ofthebook.onthethirdday,heread9/20ofthebook.thenthereare()pagesinthebook.

郭莹晖回答:
  第一天读了25页,第二天读了余下的2/5,第三天读了总页数的9/20.一共读了三天.   设这本书一共有x页.   则25+(2/5)(x-25)+(9/20)x=x   解得x=100页
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