How many 4 digit codes are possible using 5 numbers?

Answer 1

5 choose 4

=5! / (4! 1!)

=5! / 4!

= 5

EX. 1 2 3 4 5

1 2 3 4

1 2 3 5

1 2 4 5

1 3 4 5

2 3 4 5