SOLUTION: How many four letter code words can be formed using a standard 26 letter alphabet if repetition is allowed? and then if repetition is not allowed?

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Any of 26 letter can be in any of 4 spots, so there are 26^4 = 456,976 possibilities
If there is no repeating, then the answer is less, because, even though 26 letters can be first, only 25 can be second, 24 can be third, and 23 can be last, so we get
26 x 25 x 24 x 23 = 358,800 possibilities