We choose randomly a subset $\mathit S$ of size 25 from the set $\{ 1,2,...,100\}$ , what is the expected value of number of Consecutive numbers in $\mathit S$?
Consecutive numbers in $\mathit S$: is a pair $\{ i,i+1\}$ where i$\in$$\mathit S$ and i+1$\in$$\mathit S$.