[求助]gmatprep 二道题

sarahlinyu01

做PREP TEST 1有两题想不清楚,请大家帮忙解解.谢谢!
1,what fraction of this year's graduation students at a certain college are males?
(1)of this year's graduation students, 33%of male and 20% of female transferred from another college
(2)of this year's graduation students, 25% transferred from another college
2, the rate of a certain chemical reaction is derectly proportional to the square of the concentration of chemical A present and inversely proportional to the concentration of chemical B present.If the concentration of chemical B is increased by 100%, which of the follwing is closest to the percentchange in the concentration of chemical A required to keep the reaction rate unchanged.(the answer is 40%)

hitlzc

1。设X个男的，Y个女的。

1）和2）综合得35%X+20%Y=25%(X+Y)

10%X=5%Y

Y=2X

男得所占比例X/(X+Y)=X/3X=1/3

2.http://forum.chasedream.com/dispbbs.asp?BoardID=22&ID=149128

sarahlinyu01

thanks a lot!

tanaka_he

说说我的思路吧（请NN指正^^）

条件（1）(2）单独都不sufficient

转而看条件（1）+（2）=已知transferred 过来的男女生比例和transferred过来的总人数

但是不知到 未transferred过来学生的男女生比例

所以无法判断总体的男女生比例

winnie8138

1 应该是能算得，因为求的是比例，条件也是比例，而且条件里就有和总数的比例。

lijiahui0422

设男生数比总数为x   x*0.33+(1-x)*0.2=0.25

alan722

如果李宇春不是这个学校毕业的话，那第一题应该选C