What is the probability of these events when we randomly select a permutation of 1,2,....,n where n>=4

a) 1 precedes 2

I have no idea how to do this one

b) 1 immediately precedes 2

This one is simple I think. I just considered 1 and 2 as one unit to be permuted with the rest of the numbers and I get (n-1)!/n!= 1/n

I could really use some advice, thank you so much!!