Say the code were 4 numerical digits. That means each position can only have 10 possible entries: 0, 1, 2, 3, 4, 5, 6, 7, 8, or 9. So there are 10x10x10x10 = 10,000 different codes possible.

In your case, there are 26 choices for each letter slot and 10 choices for each number slot.

For the other problems, all that changes is the number of possibilities for a particular slot. In the case of number 3, if you take away A as a possible letter, that leaves only 25 possibilities for the second slot.

The probability of something happening is calculated by taking all the *desired* outcomes and dividing by all the *possible* outcomes (i.e., dividing by the answer to part 1).

1. There are 26 letters in the alphabet

The numbers are 0 – 9

so the formula to figure out the number of possible codes is 26 X 26 X 10 X 10

2. Solve the equation and use the info to answer the questions