How many different codes are possible? Answer:
How many codes are possible if repeating letters and digits is not allowed? Answer:
How many codes are possible if repeats are not allowed and the second letter must be 'U' and the fourth digit must be '2'? Answer:
If the wrong code is entered the vault automatically locks and the alarm sounds. Suppose repeating letters and digits are allowed in the code. What is ther probability of a thief breaking into the vault if the thief has no prior knowledge of the secret code? Answer:
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