If John, Trey, and Miles want to know how’ | many two-letter secret codes there are that don't have a repeated letter. For example, they want to : cou

Anish Buchanan 2021-05-05 Answered
If John, Trey, and Miles want to know how’ | many two-letter secret codes there are that dont
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timbalemX
Answered 2021-05-06 Author has 108 answers
Trey and Miles are correct — we can either use the reasoning “we do not want for the two letters to be the same, so for the first letter we have 26 choices and for the second we have 25”, so we get 26-25, or we can find the number of all two-letter codes, which we have 26-26, and subtract the number of two-letter codes with a repeated letter, which we have 26.
Adding 26 and 25 makes no sense, since for each choice of the first letter we have 2% additional codes.
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