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题库 / Prep2007E1-DS-10
Of the 800 students at a certain college, 250 students live on campus and are more than 20 years old. How many of the 800 students live on campus and are 20 years old or less?
(1) 640 students at the college are more than 20 years old.
(2) 60 students at the college are 20 years old or less and live off campus.
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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条件2 old or less是指小于20岁，不是大于或者小于20岁
其实不知道题目中的条件“有250个既住校又超过20岁的学生”也可以求解。
设x为住校且不到20岁学生是人数。
x+640+60=800
x=100
800学生是at a certain college
画个那个表格就能得出，只有1+2才可以
假设group1=students live on campus,group2=students more than 20 years old
800=group1+group2+neither-both
800=group1+640+60-250
group1=350
350-250=100