Latest TCS Aptitude Question SOLUTION: What is the probability that when 4 letters are placed in 4 addressed envelope,all r wrongly placed?

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What is the probability that when 4 letters are placed in 4 addressed envelope,all r wrongly placed?

Asked In TCS xyz (12 years ago)

Solved Bunny Read Solution (8)

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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 it means in envelop 1 there is 1st letter, in 2 there is 2nd letter ..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 enjoy :)

Is this solution Helpfull? Yes (14) | No (3)  

surojit saha  (12 years ago)

there is one formula
n!(1/2!-1/3!+1/4!)
4!(1/2!-1/3!+1/4!)
24*9/24=9 is the ans...

Is this solution Helpfull? Yes (6) | No (5)  

Bunny  (12 years ago)

All Are Wrongly Placed(Or) None Is Correctly Placed Both Is Same Na...So Probability Will Be (1/2!)-(1/3!)+((1/4!)=3/8

Is this solution Helpfull? Yes (5) | No   

Himanshu Mittal  (12 years ago)

it is a derangement question. for which formula is 4!(1-1/1!+1/2!-1/3!+1/4!)=9

Is this solution Helpfull? Yes (3) | No (4)  

swetha N  (12 years ago)

probability of keeping 4 letters is 2^4=16
in dat, crct way is 1.
so, wrong ways are 2^4-1=15

Is this solution Helpfull? Yes (1) | No (9)  

pratit khare  (12 years ago)

prob can never be greater than 1.
prob that letter is put in correct envelope is 1/4.
so ans is 1-1/4=3/4

Is this solution Helpfull? Yes (1) | No (3)  

Suresh  (12 years ago)

nCr=n!/r!(n-r)!
Hence 4C4=12/12(1)=1 where 0!=1

So the probability is 1.

Is this solution Helpfull? Yes | No (3)  

shahbaz  (12 years ago)

probability can never be greater than 1 then how it could be 16 or 9.
total outcomes=16
favourable outcomes=1(becouse there can only be 1 situation in which all the 4 letters are wrongly placed).
so the probability=1/16.

Is this solution Helpfull? Yes | No (3)  

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