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.

ANS: C

請教這題思路,謝謝^_^

200-20*2=160

100-20=80

1*80=80

160-80=80

80/2=40(3 book)

80-40=20(1 book)

1*80=80

160-80=80

80/2=40(3 book)

80-40=20(1 book)

這部份看不太懂耶,可以用文字敘述一下嗎?謝謝^_^

我想出來了,因為剩下的80人中,只能"有人買1本有人買3本",不可能都買3本或1本.

設,3本x人,1本y人,則(1)x+y=80 (2)3x+y=160,聯立可求解.

所以答案為(C)