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Password Problems
Combinatorics
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attempts
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valid passwords
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Three Digits Known
How many passwords do you need to try to be sure to find the correct one?
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attempts
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Two Digits Known
How many passwords do you need to try now?
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attempts
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All Passwords
How many different 4-digit passwords can you create in total?
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attempts
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Palindromes
How many palindromic passwords are there in total?
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attempts
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Repeaters (ABAB)
How many repeating passwords (ABAB pattern) are there in total?
Unsafe Passwords
How many total unsafe passwords are there (palindromes and repeaters together)?
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attempts
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valid passwords
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Screen Traces
How many passwords must you try at minimum to be sure to guess the correct one? (Variant with digits 4, 5, 7, 8)
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attempts
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School Number
How many passwords contain "56" consecutively?
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attempts
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Without 5 and 6
How many passwords do NOT contain the digits 5 and 6?