[求助]请教那道经典的剧院题--前20排后15排的问题

我用题号搜索，但是搜出来的是另一道题，只能这样问啦～～，请帮忙解答一下吧～～

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.

Answer: E

不是很明白这道题的解题思路。。。请各位赐教。

一共有25排：Theater M has 25 rows

条件1 说前20排的平均空置率是10个/排

条件2说后15排的平均空置率是20个/排

由上，当然无法计算，选E  

(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.

谢谢，是不是像这种题目，只有第二个条件改成：后5排的平均空置率是20个/排，才能共同由两个条件计算出来（然后选C）？

自问自答：这是在另一个testmagic的论坛上搜到的答案：

Theater problem:
----------------

Stmt1uring the show, there was an average (arithmetic mean) of 10 unoccupied seats per row for the front 20 rows.

Obviously insufficient because we don't know anything about the occupancy of the last 5 rows. INSUFF

Stmt2: During the show, there was an average (arithmetic mean) of 20 unoccupied seats per row for the back 15 rows.

Again insufficient because we don't know anything about the occupancy of the first 10 rows.

Stmt1 & Stmt2:
We know the occupancy of rows 1-20 from Stmt1 and the occupancy of rows 11-25 from Stmt 2. But we don't know what the occupancy rate of the overlap between the two statements (i.e. rows 11-20) is.
INSUFF

Ans: E