Respuesta :
Answer:
43.46% probability that the person will need to wait at least 9 minutes total
Step-by-step explanation:
To solve this question, we need to understand conditional probability and the exponential distribution.
Conditional probability:
We use the conditional probability formula to solve this question. It is
[tex]P(B|A) = \frac{P(A \cap B)}{P(A)}[/tex]
In which
P(B|A) is the probability of event B happening, given that A happened.
[tex]P(A \cap B)[/tex] is the probability of both A and B happening.
P(A) is the probability of A happening.
Expontial distribution:
The exponential probability distribution, with mean m, is described by the following equation:
[tex]f(x) = \mu e^{-\mu x}[/tex]
In which [tex]\mu = \frac{1}{m}[/tex] is the decay parameter.
The probability that x is lower or equal to a is given by:
[tex]P(X \leq x) = \int\limits^a_0 {f(x)} \, dx[/tex]
Which has the following solution:
[tex]P(X \leq x) = 1 - e^{-\mu x}[/tex]
The probability of finding a value higher than x is:
[tex]P(X > x) = 1 - P(X \leq x) = 1 - (1 - e^{-\mu x}) = e^{-\mu x}[/tex]
In this question:
Event A: Waited at least 4 minutes.
Event B: Waiting at least 9 minutes.
The length of time for one individual to be served at a cafeteria is an exponential random variable with mean of 6 minutes.
This means that [tex]m = 6, \mu = \frac{1}{6}[/tex]
Probability of waiting at least 4 minutes.
[tex]P(A) = P(X \geq 4) = P(X > 4)[/tex]
[tex]P(A) = P(X > 4) = e^{-\frac{4}{6}} = 0.5134[/tex]
Intersection:
The intersection between a waiting time of at least 4 minutes and a waiting time of at list 9 minutes is a waiting time of 9 minutes. So
[tex]P(A \cap B) = P(X > 9) = e^{-\frac{9}{6}} = 0.2231[/tex]
What is the probability that the person will need to wait at least 9 minutes total
[tex]P(B|A) = \frac{0.2231}{0.5134} = 0.4346[/tex]
43.46% probability that the person will need to wait at least 9 minutes total
