Question

How many different four-digit numbers can be made using the digits 1, 2, 3, 4, 5, 6 if no digit can be used more than once?

Answer 1

To solve this problem you must use Permutation:

You want to made 4 digit numbers with the digits 1, 2, 3, 4, 5, 6 and no digit can be used more than once. So, we have:

(A,B,C,D)

A can variate in six (6) differents forms.
B can variate in (6-1)=5 differents forms.
C can variate 4 digits.
D can variate 3 digits.

Keeping this on mind, we have:

=6!/2!
=6*5*4*3
=360

The answer is: 360