PP PS 2 Q 167

[nemolee]

167. 18146-!-item-!-187;#058&011731
In a survey of 248 people, 156 are married, 70 are self-employed, and 25 percent of those who are married are self-employed. If a person is to be randomly selected from those surveyed, what is the probability that the person selected will be self-employed but not married?


(A) 1/8
(B) 4/31
(C) 117/248
(D) 1/4
(E) 31/117

ANS is A

這題自己求出是 8個人是self-employed but not married...
我ㄉ錯誤的想法是這樣的：
156人未婚，其中是有 62人是self-employed ( 248 x 25% = 62)
題目又說已婚與未婚的一共有 70人是 self-employed
所以 70-62 = 8 人 產出這樣的答案.. ><

可是答案是 1/8... why ?? 那裡想法錯了.. 請指教....謝~

[Huang Hsin-Yi]

167. 18146-!-item-!-187;#058&011731
In a survey of 248 people, 156 are married, 70 are self-employed, and 25 percent of those who are married are self-employed. If a person is to be randomly selected from those surveyed, what is the probability that the person selected will be self-employed but not married?


(A) 1/8
(B) 4/31
(C) 117/248
(D) 1/4
(E) 31/117

ANS is A

這題自己求出是 8個人是self-employed but not married...
我ㄉ錯誤的想法是這樣的：
156人未婚，其中是有 62人是self-employed ( 248 x 25% = 62)
題目又說已婚與未婚的一共有 70人是 self-employed
所以 70-62 = 8 人 產出這樣的答案.. ><

可是答案是 1/8... why ?? 那裡想法錯了.. 請指教....謝~

你弄錯了題目意思,它是說156結婚的人25%是self-employed
therefore we get 156*25%=39 marry&self
70-39=31 not marry&self
31/248=1/8

[nemolee]

哈... 真是自己眼花.... 沒看清楚... 多謝提醒