peace on you all. I have this problem now i don't know how he reached to the final from i'm not good at math in some things so i couldn't understand the proof. this is the problem. Know about the expected value i will write down some notes i concluded from my previous blog.

1- the problem want's the expected minimum value in a k-element subset of [1, 2, ..., n].

2- i see that i have 3 element at each subset and my array [1, 2, ..., n] has n element in it does it mean i have 1/3 chances to get minimum element at array of size n so n * (1/k). Now that what i could reach to compare it to the final from of the prof of this problem But the final form is equal to (N+1)/(K+1) of this function F(N, K).

any explanation but with some easy prof. cause i didn't understand by math(words).

thanks for your time.