The total probability is 8*7=56 (the first person has 8 possibilities and the second person has 7 possibilities).
Then, taking two runways as a whole, there are seven possibilities for one runway (1.2,2,3 ... 7.8).
It's another way for two people to exchange places.
So a * * * has 7*2= 14 kinds.
So the probability is 14/56= 1/4.