Question

a personal identification number consists of 3 letters followed by 3 digits (0-9). the letters x,y and z are not used and the last digit cannot be 0 or 9. how many different identification numbers are possible?

Answer 1

The English alphabet consists of 26 letters, but since x, y and z are not used, we'll have 23 letters to choose from. From 0 to 9, there are 10 numbers total, but there's restriction that the last digit cannot be 0 or 9, so that's 8 numbers total to choose from for the last digit.

Assuming repetition is ALLOWED:
23 * 23 * 23 * 10 * 10 * 8 = 9733600