[情報] PP1-DS-20
A certain one-day seminar consisted of a morning session and an afternoon
session. If each of the 128 people attending the seminar attended
at least one of the two sessions, how many of the people attended
the morning session only?
(1) 3/4 of the people attended both sessions.
(2) 7/8 of the people attended the afternoon session.
答案: B
我看解答是說
(2)算出所有參加下午的112人,再用128人減去即可知人數16人為答案
可是題目不是說至少參加一個時段(可能兩個都參加呢?)
我的想法是由(1)算出both的96人
(2)算出下午的112人
可以利用排容原理
全部-n(A聯集B)= 全部-n(A)-n(B)+n(A交集B)
早上的就是112+X-96=128,X即為早上之人數
不之這樣哪裡有錯 所以我就選到C了
感恩~
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