请教: 2道数学题

Prep Test1_8:

What fraction of this year's graduating students at a certain college are males?

(1) Of this year's graduating students, 33% of the males and 20% of the females transferred from another college.

(2) Of this year's graduating students, 25% transferred from another college.

A Statement (1) alone is sufficient, but (2) alone is not sufficient.

B Statement (2) alone is sufficient, but (1) alone is not sufficient.

C Both statments together are sufficient, but neither statemetn alone is sufficient.

D Each alone is sufficient.

E (1) and (2) together are not sufficient.

[Answer C]

31.

Alice's take-home pay last year was the same each month, and she saved the same fraction of her take-home pay each month.  The total amount of money that she had saved at the end of the year was 3 times the amount of that portion of her monthly take-home pay that she did not save.  If all the money that she saved last year was from her take-home pay, what fraction of her take-home pay did she save each month?

A 1/2

B 1/3

C 1/4

D 1/5

E 1/6

[Answer D]

Thanks.

第一题，设共有男生m人女生f人 求m/(m+f)

(1)转校生共有 33%*m + 20%*f 无等式关系，不充分

（2）转校生共有25%*（m+f) 无等式关系，不充分

（1）+（2）33%*m + 20%*f=25%*（m+f) 可以求出m:f的ratio,然后求出m/(m+f)

第二题，设每月存的比例为a 每月收入X

12*a*X=3*(1-a)*X

a=1/5