Question

Ethan forgot the four-digit code to the lock on his briefcase. However, he did remember that the first digit is 9 and the last digit is either 5 or 4. The middle digits could be any number from 0 through 9 inclusive. What is the greatest number of four-digit codes Ethan might have to try in order to to open his briefcase?

Answer 1

We've got the first number, so now we need the others.
There is 1 possibilty for the first digit, 10 for the middle ones, and 2 for the last one.
1*10*10*2=200
200 possible codes for this briefcase