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