求助一道gwd数学

Q21:

DS: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.

the key is E.

这道试题我也模糊的觉得是选E,但是无法用明确的方法说明如何选E的

哪位可以指教,明确的排除C?

个人觉得，可以把前10排未占用的座位设成x，中间10排的设成y，最后5排设成z。

根据一，二两个条件，可以列出方程：

10=(x+y)/20

20=(y+z)/15

两个方程，三个未知数，答案就不唯一了吧

恩,同意LS的解答,中间的10排是不确定因素,选E

哦,是这样,明白了,谢谢~~