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प्रश्न
A person writes 4 letters and addresses 4 envelopes. If the letters are placed in the envelopes at random, then the probability that all letters are not placed in the right envelopes, is
पर्याय
\[\frac{1}{4}\]
\[\frac{11}{24}\]
\[\frac{15}{24}\]
\[\frac{23}{24}\]
उत्तर
4 letters can be placed in 4 envelopes in 4! ways = 24 ways
Now, there is only one method, by which all the letters are placed in the right envelope.
P(all letters are placed in the right envelopes) = \[\frac{1}{24}\] P(all letters are not placed in the right envelopes) = 1 - P(all letters are placed in the right envelopes)
\[ = \frac{23}{24}\]
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