10 4. 10 9 8 7 6 5 4 3 2 1 6 5 4 3 2 1 5040. If you are not familiar with the n.
In general if there are n objects available.
C n r n. Find the number of subsets of the set 1 2 3 4 5 6 7 8 9 10 having 3 elements. R times nr. Therefore you divide the permutations formula by in order to eliminate the redundancies.