Imagine that all and each line are marked by the first 13 letters of English alphabet:
1 2 3 4 5 6 7 8 9 10 11 12 13
A B C D E F G H I J K L M
Then the space of all possible events is the set of all 3-letter words comprising of these letters.
Repetitions of letters in these words are allowed.
It is easy to calculate the number of all such 3-letter words.
Any of 13 letter can stay in the 1-st position. This gives 13 opportunities.
Any of 13 letter can stay in the 2-nd position. This gives 13 opportunities.
Any of 13 letter can stay in the 3-rd position. This gives 13 opportunities.
In all, there are such words.
Correspondingly, there are elements in the space of events, in all.
Now, the favorable events are those 3-letter words what have no repetitions.
The number of such words is exactly 13*12*11 = 1716.
Therefore, the probability under the question is equal to
= 0.7811 = 78.11% (approximately). ANSWER
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Very similar to the problem 4 of the lesson
- Selected probability problems from the archive
in this site.
Also, you have this free of charge online textbook in ALGEBRA-II in this site
- ALGEBRA-II - YOUR ONLINE TEXTBOOK.
The referred lesson is the part of this online textbook under the topic "Solved problems on Probability".
Save the link to this textbook together with its description
Free of charge online textbook in ALGEBRA-II
https://www.algebra.com/algebra/homework/complex/ALGEBRA-II-YOUR-ONLINE-TEXTBOOK.lesson
into your archive and use when it is needed.