How many combinantion of 2 numbers are there in 10

to perm ten numbers

C(10,2) = 45 where C(n,k) is binomial coefficient.
P(10,2) = 90 where P(n,k) gives the number of k-permutations of {1, 2, ... , n}.

Your question is not clear, but I guess you mean one or both of these quantities.