The consecutive numbers can be (1,2) (2,3) (3,4) (4,5). Usually consecutive things are n-1. Like you had to select consecutive numbers out of 5 numbers. So cases of consecutive numbers are 5-1 = 4

Now no, of ways of selecting 2 numbers out of 5 = ^{5}C_{2} = 10.

So probability = 4/10 or 2/5