. The probability that two specified letters will be placed in the correct envelopes is 1[n(n – 1)]. The probability that none of the othern – 2 letters will then be placed in the correct envelopes is qn-2. Therefore, the probability that only the two specified letters, and no other letters, will be placed 1 in the correct envelopes is It follows that the probability that exactly two of the n n(n – 1) letters will be placed in the correct envelopes, without specifying which pair will be correctly placed,

A First Course in Probability (10th Edition)
10th Edition
ISBN:9780134753119
Author:Sheldon Ross
Publisher:Sheldon Ross
Chapter1: Combinatorial Analysis
Section: Chapter Questions
Problem 1.1P: a. How many different 7-place license plates are possible if the first 2 places are for letters and...
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. The probability that two specified letters will be placed in the correct envelopes is 1[n(n – 1)]. The
probability that none of the othern – 2 letters will then be placed in the correct envelopes is qn-2.
Therefore, the probability that only the two specified letters, and no other letters, will be placed
in the correct envelopes is
1
-¶n-2. It follows that the probability that exactly two of the n
п(п — 1)
letters will be placed in the correct envelopes, without specifying which pair will be correctly placed,
Transcribed Image Text:. The probability that two specified letters will be placed in the correct envelopes is 1[n(n – 1)]. The probability that none of the othern – 2 letters will then be placed in the correct envelopes is qn-2. Therefore, the probability that only the two specified letters, and no other letters, will be placed in the correct envelopes is 1 -¶n-2. It follows that the probability that exactly two of the n п(п — 1) letters will be placed in the correct envelopes, without specifying which pair will be correctly placed,
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