GWD 18-13

[ariesmilla]

好像沒有討論過，討論區沒有這題...
Q13:
Each of 20 parents chose one of five days from Monday through Friday to attend parent-teacher conferences. If more parents chose Monday than Tuesday, did at least one of the parents choose Friday?
(1) None of the five days was chosen by more than 5 parents.
(2) More parents chose Monday than Wednesday.

為什麼只要知道A就足夠了呢? None of the five days was chosen by more than 5 parents 只不超過五，但包括五嗎?...突然秀逗了...
感謝~~

[pamelatsai]

20parents/4 days=5 parents per day
可知如果一星期中每天都有5個parents 註定一天會沒有人~~
條件一說none of the five days was chosen by more than 5 parents
降Friday有可能沒人選~
但是題目有講到說more parents choose Monday than Wednesday~
則可知結合條件(1)可知~~星期一最多5人 假設星期三是4人
星期二星期四就算最多5 人 就一定有一個人要選星期五了~~
所以(A)充分~

[ariesmilla]

原來是這樣，理解了，真是謝謝你:D