GWD18-13

[EmmaCYC]

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.


答案A

請問此提怎解?

[scujean]

令n（一）：選星期1的家長人數
由題目：n（一）> n（四）
由1：n（一）~ n（伍）每個都最多等於5 加上條件1, n（一）=5且n（二）=5且n（三）=5且n（四）=4
n（伍）=20-5-5-5-5-4=1
由2：若n（一）=20, n（伍）=0
但是有其他很多種解法，可以讓n（伍）>1