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Stolb23 [73]
2 years ago
7

A class of 10 students hang up their coats when they arrive at school. Just before recess, the teacher hands one coat selected a

t random to each child. What is the expected number of children who get his or her own coat?
Mathematics
1 answer:
Fittoniya [83]2 years ago
6 0

Answer:

0.1274

Step-by-step explanation:

Let X be the random variable that measures the number of children who get their own coat.

Then, the expected value of X is

E[X] = 1P(X=1) + 2P(X=2)+3P(X=3)+...+10P(X=10)

The probability that a child gets her or his coat is

P(X=1) = 1/10

To compute the probability that 2 children get their own coat, we notice that there are 10! possible permutations of coats. The two children can get their coat in only one way, the other 8 coats can be arranged in 8! different positions, so the probability that 2 children get their own coat is

P(X=2) = 8!/10! = 1/(10*9)  and

2P(X=2) = 2/(10*9)

Similarly, we can see that the probability that 3 children get their own coat is

P(X=3) = 7!/10! = 1/(10*9*8) and  

3P(X=3) = 3/(10*9*8*7)

and the expected value of X would be

E[X] = 1/10 + 2/(10*9) + 3/(10*9*8)+...+10/10! = 0.1274

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