Latest self Aptitude Question SOLUTION: Four letters are to be placed in four addressed envelopes. If the letters are placed at random into the envelopes, find out the following probabilities. The probability that none

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(#M40002265) SELF General Ability question Keep an EYE

Four letters are to be placed in four addressed envelopes. If the letters are placed at random into the envelopes, find out the following probabilities.

The probability that none of the letters are placed in the right envelopes is:

a) 1/24

b) 3/8

c) 23/24

d) 13/24

e) None of the above

Ranjit (12 years ago)

Unsolved Read Solution (4)

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virendra  (12 years ago)

the ans is: 3/8

Total no. of ways to put the letters in the envelop is !4= 24

all letters are wrongly placed..
suppose the letters are 1,2,3,4
if i write 1234 its mean in envelop 1 there is 1st letter, in 2 there is 2nd..so on

there would be 9 such combination to put the letters in the wrong envelop:
2143, 2341, 2413
3142, 3412, 3421
4123, 4312, 4321

so 9/24= 3/8 :)

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Dineshlal  (12 years ago)

Ans: 3/8
Soln: for n letters not placed in correct envelope = (1/2!)-(1/3!)+(1/4!)-...+(1/n!)
so for 4 letters ans is 3/8...

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Bunny  (12 years ago)

This Is The Case Of Dearrangement...So None Are Placed Is (1/2!)-(1/3!)+(1/4!)=3/8

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Subhradip Biswas  (12 years ago)

ans..c)
total no. of case n(s)=4!=24
no of enent n(e)=1
probability of placing letters in right envelope=n(e)/n(s)=1/24
so,...probability of not placing =(1-1/24)=23/24

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