Respuesta :
Answer:
44.93% probability that the person will need to wait at least 7 minutes total
Step-by-step explanation:
To solve this question, we need to understand the exponential distribution and conditional probability.
Exponential 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]
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.
The length of time for one individual to be served at a cafeteria is an exponential random variable with mean of 5 minutes
This means that [tex]m = 5, \mu = \frac{1}{5} = 0.2[/tex]
Assume a person has waited for at least 3 minutes to be served. What is the probability that the person will need to wait at least 7 minutes total
Event A: Waits at least 3 minutes.
Event B: Waits at least 7 minutes.
Probability of waiting at least 3 minutes:
[tex]P(A) = P(X > 3) = e^{-0.2*3} = 0.5488[/tex]
Intersection:
The intersection between waiting at least 3 minutes and at least 7 minutes is waiting at least 7 minutes. So
[tex]P(A \cap B) = P(X > 7) = e^{-0.2*7} = 0.2466[/tex]
What is the probability that the person will need to wait at least 7 minutes total
[tex]P(B|A) = \frac{0.2466}{0.5488} = 0.4493[/tex]
44.93% probability that the person will need to wait at least 7 minutes total
