问几题数学，GWD上的，望好心人解答~

crusaderma

Last year in a group of 30 businesses, 21 reported a net profit and 15 had investments in foreign markets. How many of the businesses did not report a net profit nor invest in foreign markets last year?
(1) Last year 12 of the 30 businesses reported a net profit and had investments in foreign markets.
(2) Last year 24 of the 30 businesses eported a net profit or invested in
                                                   Answer:
答案否定了1，所以选B，而我选的是D。

-- by 会员 茶色的秋天 (2011/10/27 18:57:29)

这道题应该选 D, 其实(1) 跟 (2)应该就是一个条件
---------------------------------------------
********    | Profit | No Profit | TOTAL   |
---------------------------------------------
Invested     |     a     |          b     |    15       |
---------------------------------------------

Not invted |      c    |        x      |      15      |
---------------------------------------------

Total           |  21    |        9        | 30          |
---------------------------------------------



(1) 给了你 a = 12
所以知道  c = 9, ==> x = 6
sufficient
(2) 知道last year 24 of the 30 businesses reported a net profit or invested inforeign markets, or both.
也就是说，我们知道
21 + 15 - both = 24
所以both = 12, 就是条件(1)
所以sufficient
应该选 D

浩宇

gwd上的第一题貌似选E阿