[求助]请教涛涛29-9题

tayleerchen2

请教涛涛29-9题

Q9:

A total of 100 customers purchased books at a certain bookstore last week.  If these customers purchased a total of 200 books, how many of the customers purchased only 1 book each?

(1)   None of the customers purchased more than 3 books.

(2)   20 of the customers purchased only 2 books each.

                  

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.

答案选C,我觉得应该选A

windlake

A? 有可能50人每人只买1本，或者没人只买1本，100人每人买2本啊

liuhongjuan

"None of the customers purchased more than 3 books"到底是什么意思?

我理解为"没人买3本以上的书,每个人最多买3本",这样的话是不是应该选E?
还是我理解错了............?

结合条件(1)和(2)考虑,就是说"80人买了160本书,问买1本书的有多少人?"
80×2=160
78×2+3+1=160
76×2+3×2+1×2=160
...... ......
买1本书的人数不确定啊!

liushuixian

“None of the customers purchased more than 3 books”意思是没

顾客购买的书本数超过3本，即有的顾客买1本，有的顾客买2本，有的顾客

买3本

设买1本的顾客有x人，买2本的顾客有y人，买3本的顾客有z人……

(1) x+2y+3z=200且x+y+z=100，三元一次方程要有三个方程式才能求得结

果，不充分

(2) 只知买2本的人数，不知其他人买多少本，不充分

(1)+(2) ： x+2*20+3z=200且x+20+z=100，多了条件(2)，变成二元一次方

程，两个方程式可求，充分

选C

tayleerchen2

谢谢.明白了:"20 of the customers purchased only 2 books

each."意思是"only 20 of the customers purchased only 2 books

each.",而不是"at least 20 of the customers purchased only 2 books

each."