We have 28 ways to choose the first speaker, 27 ways to choose the second speaker, etc.
So...the total number of ways to choose 4 speakers is 28 x 27 x 26 x 25 = 491,400
For the second, we have 4! ways of arranging any 4 speakers = 24
Considering that John and Sam can be arranged two ways, either John first and Sam second, or vice-versa, and they can fill any of three positions.... (1,2) (2,3)(3,4)...then 2 x 3 = 6 arramgements. And for each of these the other two people can be arranged in two ways. So, 6 x 2 = 12 arrangements
So the probability that they speak next to each other is 12 arrangements/24 possible arrangements = 1/2 = 50%.
