Question 885013
<pre>
Choose the most restrictive digit first, which is the last digit.

Choose the last digit 1 way (as 0)
Choose the first digit any of the 5 remaining ways. 
Choose the second digit any of the 4 remaining ways.
Choose the third digit any of the 3 remaining ways.
Choose the fourth digit any of the 2 remaining ways.

Answer: 1x5x4x3x2 = 120 ways

Edwin</pre>