大家帮帮忙啊！！！两道类似PP题，一时转不过弯！！

jesmine

有两道相似的数学题，我弄混了，大家有时间的话帮我看看可以不？
What fraction ofthis year's graduating students at a certain college are males?
(1)  Of this year's graduating students, 33percent of the males and 20 percent of the females transferred from anothercollege.
(2)  Of this year's graduating students, 25percent transferred from another college.
【答案】C

{思路】(1)0.33M+0.2F=transfer 不充份           (2) 0.25（M+F)=transfer 不充份
         
(1)+(2) M=5/8F 充份選C

If 2/5 of the students atCollege C are business majors, what is the number of female students at CollegeC ?
(1)  2/5of the male students at College C are business majors.
(2)  200 of the female students at College C are business majors.


为什么这道题不能选B？运用上面一道题目的方法，不是一样可以：2/5（m+f）=2/5m+2/5f,而2/5f=200,这样不就可以解出来了吗？

我想我错在“男女组成的比例是未知的”，但是我就是转不过弯来？有哪位好心的CDer给我解释下不？？？

jesmine

为什么没人理我啊··？、呜呜呜····

chris8849

What fraction ofthis year's graduating students at a certain college are males?
(1)  Of this year's graduating students, 33percent of the males and 20 percent of the females transferred from anothercollege.
(2)  Of this year's graduating students, 25percent transferred from another college.
可求出全校的男女人数比例
If 2/5 of the students atCollege C are business majors, what is the number of female students at CollegeC ?
(1)  2/5of the male students at College C are business majors.
(2)  200 of the female students at College C are business majors.
你要求这个学校的总女生数 就要知道这个系有多少人和这个系女生占学校总女生数的比例 因此2不行 2只告诉你了人数 而且条件中是business Major的总比例数 这个说明不了女生的比例