GWD管卫东GMAT 第7套题 数学第21题 求讲解 谢谢 正确答案是E 我觉得C……

题目

GWD管卫东GMAT 第7套题 数学第21题 求讲解 谢谢 正确答案是E 我觉得C……
Q21:
Theater M has 25 rows with 27 seats in each row. How many of the seats were occupied during a certain show?
(1) During the show, there was an average (arithmetic mean) of 10 unoccupied seats per row for the front 20 rows.
(2) During the show, there was an average (arithmetic mean) of 20 unoccupied seats per row for the back 15 rows.

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
D. EACH statement ALONE is sufficient.
E. Statements (1) and (2) TOGETHER are NOT sufficient.

答案

M剧场有25排座位,每排有27个座位.问在一场表演中究竟多少个座位被占了.
条件1：前20排座位每排空座的算术平均值为10
条件2：后15排座位每排空座的算术平均值为15
哥们你说是C,那么麻烦你列出你的式子.我怀疑你没有算就直接选C了.
条件1能得出前20排occupied的seats是：（27-10）*20
条件2能得出后15排occupied的seats是：（27-20）*15
但不能得出后5排的occupied的seats,因为已知的条件给的是平均数,没法算出部分的具体数.就是说,你画个集合大饼图,这里有个交集算了两次,你必须减去一次的才能得出最终答案.
所以,两个条件加在一起也得不出整个25排的 occupied seats ,所以选E