Access codes for a lockbox consist of four digits. The fist and last digits cannot be zero. How many different codes are available?

Question

What is the set up and work on how to solve the problem 

Answer 1

 

9 * 10* 10 * 9=8100

Because the first and last digits can be 1-9, nine options. The middle digits can be 0-9, ten options. Fundamental counting principle says you multiply all options.