We have a password with length of 6 characters, out of a possible 27 letters, 10 digits and 8 special characters.
My questions are:
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A: How many possible combinations there are?
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B: How many combinations have at least two same characters?
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C: How many combinations have at least one special character?
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D: How many combinations have exactly two same characters (and others are different characters)?
The answer to A is $(27+10+8)^6$ but B, C and D are a mystery to me. Could I have some advice on the problem?
Best Answer
Using this count, subtracting it away from the result from A gives the count we are interested in