[問題]GWD29-9

[amyliang]

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.
Ans:C
我選E
因為(1)顧客可以買1-3本的書 insufficient
(2)只知道買2本書的顧客的數量 insufficient

(1)+(2) 還是不充分 因為customers可以買1本或是3本...
為什麼答案會是C呢? 我那裡想錯了呢????

[Huang Hsin-Yi]

(1)(2)買3本的有x人,買2本有20人,買1本有y人
(2)由題目可知
X+Y=80
3x+Y=160

解聯立 Y=40

[amyliang]

.....謝謝...完全沒想到解聯立.....

[ccy1205]

A 就能成立

共100人買 200本書 (A)每人至多買兩本...當然每人就買2本才能剛好200本哩