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What is the probability that if 11 letters are typed, no letters are repeated?
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We have 26 lowercase letters and 26 uppercase letters in English alphabet.
Assuming that we use lowercase letters only, there are possible words
of the length 11.
Of them, the number of words with no repeating letters is 26*25*24*23*22*21*20*19*18*17*16
(11 factors of integer numbers in descending order starting from 26, in all).
The probability do not have repeating letters is
1 - =
= 1 - 0.084026 = 0.915974 (rounded). ANSWER
Solved.
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A TWIN problem to it is a popular problem on finding the probability
that there is no coinciding birthdays in the group of 11 persons.
See the lesson
- Coinciding birthdays
in this site.