2022.03.09 机经 DS 问题 _ probability

sushim

DS - A group of adults and children. They shake hands witheach other. How many adults are there?

条件一：Randomly pick 2 people, theprobability that  2 adults get picked is1/3.

条件二：randomly pick 2 people, theprobability that 2 children get picked is 4 times as the probability that 2adults get picked.

有人做了可以解释下吗？我看构筑选了E。我也觉得貌似是E，因为没法算出到底  adult 有几人

但是 结合条件1 和 2，

条件2说：randomly pick 2 people, the probability that 2 children get picked is 4 times as the probability that 2 adults get picked.

然后条件1又说：Randomly pick 2 people, the probability that  2 adults get picked is 1/3

那不是说明 randomly pick 2 people, he probability that 2 children get picked 是 4 *（1/3) = 4/3？  这都大于1了呀？

求解