Question

How many different 1, 2, or 3 digit whole numbers can be made using the digits 2,5, and 8? No digit may be repeated within 1 number.

Answer 1

With one digit you can only make three numbers, 2, 5, and 8.
With two digits, _ _  there are 3 possibilities for the first digit and 2 in the second totaling 3*2 = 6 possibilities. 
With three digits, _ _ _, there are 3 possibles in the first digit, 2 in the second and only 1 in the last. 3*2*1 = 6
Now we add all of the possibilities - 3+6+6 = 15.

Your final answer should be 15 numbers. Hope this helps!