Permutation or combination?

If you calculate the number of different ways five of the 31 students could be chosen to put problems 1,2,3,4,and 5 on the board, is this a number of combinations or a number of permutations?

At first I thought it was a number of permutations because order in which the numbers are arranged matters, but then I thought it was a combination because they are only using 5 of the 31 students. Which is right?

It is clearly a permutation problem.
You are counting the number of one-to-one functions from a set five to a set of thirty one. Each problem is assigned to exactly one student.