Respuesta :
Using the binomial distribution, it is found that:
a) The expression is [tex]\left(\frac{364}{365}\right)^{n}[/tex]
b) You need to select at least 587 people.
For each person, there are only two possible outcomes, either they share your birthday, or they do not. The probability of a person sharing your birthday is independent of any other person, hence, the binomial distribution is used to solve this question.
Binomial probability distribution
[tex]P(X = x) = C_{n,x}.p^{x}.(1-p)^{n-x}[/tex]
[tex]C_{n,x} = \frac{n!}{x!(n-x)!}[/tex]
The parameters are:
- x is the number of successes.
- n is the number of trials.
- p is the probability of a success on a single trial.
There are 365 days in a non-leap year, hence, the probability of each person sharing your birthday is [tex]p = \frac{1}{365}[/tex]
Item a:
This probability is P(X = 0), hence:
[tex]P(X = x) = C_{n,x}.p^{x}.(1-p)^{n-x}[/tex]
[tex]P(X = 0) = C_{n,0}.\left(\frac{1}{365}\right)^{0}.\left(\frac{364}{365}\right)^{n} = \left(\frac{364}{365}\right)^{n}[/tex]
Hence, the expression is [tex]\left(\frac{364}{365}\right)^{n}[/tex]
Item b:
The probability that at least one person shares your birthday is:
[tex]P(X \geq 1) = 1 - P(X = 0)[/tex]
We want that:
[tex]P(X \geq 1) \geq 0.8[/tex]
Hence:
[tex]1 - P(X = 0) \geq 0.8[/tex]
[tex]P(X = 0) \leq 0.2[/tex]
Hence:
[tex]\left(\frac{364}{365}\right)^{n} \leq 0.2[/tex]
[tex]n\log{\left(\frac{364}{365}\right)} \leq \log{0.2}[/tex]
[tex]n \geq \frac{\log{0.2}}{\log{\left(\frac{364}{365}\right)}}[/tex]
[tex]n \geq 586.6[/tex]
Rounding up: You need to select at least 587 people.
To learn more about the binomial distribution, you can take a look at https://brainly.com/question/24863377
