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Seven people go to a cinema and park their car outside,which are identical.while returning only three of them were able to unlock their cars.find total no. of ways in which this can be done

Seven people go to a cinema and park their car outside,which are identical.while returning only three of them were able to unlock their cars.find total no. of ways in which this can be done
 

Grade:12

2 Answers

Vijay Mukati
askIITians Faculty 2590 Points
6 years ago
This will be equal to selecting 3 out of 7 people and then rearrange them but subtracting one case for which the cars will be unlock. 7P3 -1.
mahein
13 Points
2 days ago
choose 3 out of 7 and dearrange rest 4 because only three of them are right so answer will be 7C3*D9=7*5*9=315
 

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