Respuesta :
Answer:
There is a 6.378% probability that the will be within $200 of the population mean.
There is a 35.569% probability that the sample mean will be greater than $9000.
Step-by-step explanation:
Normal model problems can be solved by the zscore formula.
On a normaly distributed set with mean [tex]\mu[/tex] and standard deviation [tex]\sigma[/tex], the z-score of a value X is given by:
[tex]Z = \frac{X - \mu}{\sigma}[/tex]
Each z-score value has an equivalent p-value, that represents the percentile that the value X is, or the probability that a value is LOWER than the value of X.
In our problem, we have these following informations:
The population mean is $8086. So [tex]\mu = 8086[/tex].
The population standard deviation is $2500. So [tex]\sigma = 2500[/tex]
What is the probability the sample mean will be within $200 of the population mean?
Within 200 from the the population mean is from 8086-200 through 8086+200. So from 7886 through 8286. The answer to this question is the pvalue of the zscore of [tex]X = 8286[/tex] subtracted by the pvalue of the zscore of [tex]X = 7886[/tex].
We find the pvalue of a zscore looking at the zscore table.
For X = 8286
[tex]Z = \frac{X - \mu}{\sigma}[/tex]
[tex]Z = \frac{8282-8086}{2500}[/tex]
[tex]Z = 0.08[/tex]
The pvalue of [tex]Z = 0.08[/tex] is .53188.
For X = 7886
[tex]Z = \frac{X - \mu}{\sigma}[/tex]
[tex]Z = \frac{7886-8086}{2500}[/tex]
[tex]Z = -0.08[/tex]
The pvalue of [tex]Z = -0.08[/tex] is .4681.
The probability that the sample mean will be within $200 of the population mean is
[tex].53188 - .4681 = 0.06378[/tex]
There is a 6.378% probability that the will be within $200 of the population mean.
What is the probability the sample mean will be greater than $9000?
The first step to find this probability is finding the Z-score of [tex]X = 9000[/tex]
[tex]Z = \frac{X - \mu}{\sigma}[/tex]
[tex]Z = \frac{9000-8086}{2500}[/tex]
[tex]Z = 0.37[/tex]
The pvalue of [tex]Z = 0.37[/tex] is .64431. This means that there is a 64.431% probability that the sample mean will be lesser than $9000.
The probability that the sample mean is:
100% - 64.431% = 35.569%
There is a 35.569% probability that the sample mean will be greater than $9000.