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Eight letters are to be kept in 8 envelopes. Find probability that at least one letter is kept in right envelope?
dear pratik
number of ways of at least one letter is kept in right envelope(n)
n= total ways - number of ways when all letter kept in wrong envelope
n =8! - 8![1-1/1! +1/2! -1/3! .........+1/8!]
So probability =n/8!
calculate value of n and put here
Please feel free to post as many doubts on our discussion forum as you can. If you find any question Difficult to understand - post it here and we will get you the answer and detailed solution very quickly. We are all IITians and here to help you in your IIT JEE & AIEEE preparation. All the best. Regards, Askiitians Experts Badiuddin
Thats good, but i cant understand how the "number of ways when all letter kept in wrong envelope " came as " 8![1-1/1! +1/2! -1/3! .........+1/8!] " .
Dear pratik
this is theorem proof is not in IIT JEE syllabus
If n letter are to be kept in n envelope such that no letter kept in right envelope so number of ways=
n![1-1/1!+ 1/2! -1/3! +..........(-1)n 1/n!)]
Regards
Badiuddin
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