Question 331835: You need to make a password for you computer that contains two letters and two numbers that cannot repeat. How many different passwords are possible?
Answer by jrfrunner(365)   (Show Source):
You can put this solution on YOUR website! You need passwords with WWNN without repeating the letters or numbers
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so there are 26 words to choose from, after the first word, there are 25 words left to choose. There are 10 one digit number 0 to 9, but after you select the first number there are 9 choices left.
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So WWNN = 26*25*10*9 = 58500, but.... (and there is always a but)
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there are 4! ways to rearrange these 2 letters adn 2 numbers, creating different passwords from the "same" letters and numbers.
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so the number of different passwords is 4!*26*25*10*9=1404000
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