If no digit can be used more than once, how many 5-digit numbers can be formed only using the numbers 3,8,1,2,5, and 7?

A: 350 numbers
B: 717 numbers
C: 722 numbers
D: 720 numbers

I guessed the answer 720 and got it right but I don't know why the answer is 720. Can someone please explain to me how to complete this problem?

1 answer

You can use combination.
There are 6 digits: 3, 8, 1, 2, 5, 7
So the combination digits will be:
6*5*4*3*2 = 720