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Counting Problems on Password Using Combination

1. Using only 26 capital letters of the alphabet, how many 8-letters password are possible?

2. Repeat step 1 but do not allow the same letter to be used more than once in the password?

3. Repeat steps 1 and 2 using an encryption alphabet that contains 26 uppercase letters, 26 lowercase letters, and digit 0 through 9.

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Solution Preview

Hi, this is in fact a statistical problem.

1. Since we have 26 letters, if we create a 8-letter password, the first letter of password has 26 choices, the second letter of password has 26 choices, the eighth letter of password has 26 choices. So there are 26^8 possible ...

Solution Summary

The solution gives detailed steps on counting number of passwords using the technique of combination and permutation under several conditions.