请教数学题.

oscarwang

A certain high school with a total enrollment of 900 students held a science fair for three days last week. how many of the students enrolled in the high school attended the science fair on all three days?

(1) of the students enrolled in the school ,30percent attended the science fair on two or more days.

(2)of the studens enrolled in the school, 10percent of those that attended the science fair on at least one day attended on all three days.

这类题的解题思路是什么?怎么想明白?

请赐教!!!谢谢!!

xiaojukuaipa

如果条件１变成告诉你多少ＰＥＲＣＥＮＴ一天也没参加　就可以选Ｃ

我是这样想的。．