Question

How many four-digit personal identification numbers (PIN) are possible if the PIN cannot begin or end with a 0 and the PIN must be an even number?

Answer 1

The beginning number of the pin can be any number except 0, so there are 9 choices. Both for second and third number can be any number. So there are 10 numbers possible for each placement. Lastly, for the fourth number we can only have digits 2, 4, 6, and 8 all in all 4. 
                      number of possible pins = 9 x 10 x 10 x 4 = 3600