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20 PEOPLE , OF WHICH 10 ARE DOCTORS AND 10 ARE ENGINEERS GO IN A MEETING , WHEN THEY COME OUT , THEY FIND THEIR JACKETS JUMBLED UP. WHATS THE PROBABILITY THAT NO ENGINEER GETS HIS ORIGINAL JACKET.

20 PEOPLE , OF WHICH 10 ARE DOCTORS AND 10 ARE ENGINEERS GO IN A MEETING , WHEN THEY COME OUT , THEY FIND THEIR JACKETS JUMBLED UP.
WHATS THE PROBABILITY THAT NO ENGINEER GETS HIS ORIGINAL JACKET.

Grade:12th pass

1 Answers

Dhruva Narayan
20 Points
7 years ago
there are 20 coats, so the probability of the first engineer getting his coat wrong is 19/20, as there is only a 1/20 chance of getting the coat correct. the probability of the 2nd engineer getting his coat wrong is 18/19 as he has 19 coats to chose from as the first engineer has already taken one coat. similarly the probality of the 10th engineer getting his coat wrong is 10/11. 
19/20*18/19*17/18*--------------*11/12*10/11 = 1/2

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