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题库 / Prep2007E1-DS-162
What fraction of this year's graduating students at a certain college are males?
(1) Of this year's graduating students, 33 percent of the males and 20 percent of the females transferred from another college.
(2) Of this year's graduating students, 25 percent transferred from another college.
Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
EACH statement ALONE is sufficient.
Statements (1) and (2) TOGETHER are NOT sufficient.
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没读懂题目的意思
（1)今年毕业的学生中，33%的男生和20%的女生是从别的学校转学过来的。
（2）在今年的毕业生中，有25%是从其他大学转学来的。
设男生x人，女生y人
则（1）（2）得到33%x+20%y=25%(x+y)，可以求出x与y的比例！！
当题目要求是求两个未知数的比例而不是具体数值时，只需要一个二元方程就能解出比例！！！！
设男生人数m，女生人数f
刚好可以建立一个方程
设男生x人，女生y人
1）+2）33％x + 20％y = 25％（x + y）
8％x = 5％y
x /（x + y）= 5/13