a**y 发帖数: 6501 | 1 【 以下文字转载自 OnTheRoad 讨论区 】
【 原文由 aily 所发表 】
Given 20 people, what is the probability that among the 12 months in the year
there are 4 months containing exactly 2 birthdays and 4 containing exactly 3
birthdays?
脑袋灌水了,想不出,thanks! | s*****v 发帖数: 360 | 2 a0 a1 a2 a3 a4 a5 a6 a7 .....
s0 = a0
s1 = a0 + a1
s2 = a0 + a1 + a2
...
if you know s3 and s4
then a4 = s4 - s3. |
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