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MC II-B Problem 4.29 solution wrong ?
Problem 4.29 Suppose some friends go to a party. They each wear a coat. However,
as they are leaving, they each randomly grab a coat. How many ways can the friends
leave so that none of them have their own coat, if there are 5 friends?
The week 4 solution says 76 computed as following
5!−
5! / 2!
+
5! / 3!
−
5! / 4!
+
5! / 5! = 76.
But correct answer seems to be 5! - 76 = 44 .
76 is the number of ways at least one friend grabbed his/her own coat and 44 is the number of ways no one left with their own coat.
It's easy to verify there are only 2 ways when there are 3 friends which is NOT
3! - 3!/2! + 3!/3! = 4. Instead 6 - 4 = 2 is correct.
Can someone confirm ?
Thanks.
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