How often are they actually meeting?

他们多长时间才能见到一次呀
How often are they meeting?

多长时间呢
Let's have a look.

我们来算一下
Let's go back to the previous board.

我找一下那块黑板
Here it is.

就是这块了
So they meet when they end up in this box or this box, is that right?

这两个单元格表示两人见面了对吧
So what's the probability of them ending in those boxes?

那么这两个单元格发生的概率有多大呢
Well ending up in this box is probability 2/3, 1/3

这个单元格的概率是2/3*1/3
and ending up in this box is probability 1/3, 2/3, is that right?

而这个单元格的概率是1/3*2/3
You end up meeting apple picking,

一起去摘苹果时呢
the 2/3 of the time when Nina goes there

妮娜选摘苹果的概率是2/3
times the 1/3 of the time when David goes there.

大卫选摘苹果的概率是1/3