Answer:
a) ![\sigma_{\bar X} = \frac{\sigma}{\sqrt{n}}= \frac{40000}{\sqrt{50}}= 5656.85](https://tex.z-dn.net/?f=%20%5Csigma_%7B%5Cbar%20X%7D%20%3D%20%5Cfrac%7B%5Csigma%7D%7B%5Csqrt%7Bn%7D%7D%3D%20%5Cfrac%7B40000%7D%7B%5Csqrt%7B50%7D%7D%3D%205656.85)
b) Since the distribution for X is normal then we know that the distribution for the sample mean
is given by:
c) ![P( \bar X >112000) = P(Z>\frac{112000-110000}{\frac{40000}{\sqrt{50}}}) = P(Z>0.354)](https://tex.z-dn.net/?f=%20P%28%20%5Cbar%20X%20%3E112000%29%20%3D%20P%28Z%3E%5Cfrac%7B112000-110000%7D%7B%5Cfrac%7B40000%7D%7B%5Csqrt%7B50%7D%7D%7D%29%20%3D%20P%28Z%3E0.354%29)
And we can use the complement rule and we got:
![P(Z>0.354) = 1-P(Z](https://tex.z-dn.net/?f=%20P%28Z%3E0.354%29%20%3D%201-P%28Z%3C0.354%29%20%3D%201-0.600%20%3D%200.400)
d) ![P( \bar X >100000) = P(Z>\frac{100000-110000}{\frac{40000}{\sqrt{50}}}) = P(Z>-1.768)](https://tex.z-dn.net/?f=%20P%28%20%5Cbar%20X%20%3E100000%29%20%3D%20P%28Z%3E%5Cfrac%7B100000-110000%7D%7B%5Cfrac%7B40000%7D%7B%5Csqrt%7B50%7D%7D%7D%29%20%3D%20P%28Z%3E-1.768%29)
And we can use the complement rule and we got:
![P(Z>-1.768) = 1-P(Z](https://tex.z-dn.net/?f=%20P%28Z%3E-1.768%29%20%3D%201-P%28Z%3C-1.768%29%20%3D%201-0.0385%20%3D%200.962)
e) ![P(100000< \bar X](https://tex.z-dn.net/?f=%20P%28100000%3C%20%5Cbar%20X%20%3C112000%29%20%3D%20P%28%3C%5Cfrac%7B100000-110000%7D%7B%5Cfrac%7B40000%7D%7B%5Csqrt%7B50%7D%7D%7D%3CZ%3C%5Cfrac%7B112000-110000%7D%7B%5Cfrac%7B40000%7D%7B%5Csqrt%7B50%7D%7D%7D%29%20%3D%20P%28-1.768%3CZ%3C0.364%29)
And we can use the complement rule and we got:
![P(-1.768](https://tex.z-dn.net/?f=%20P%28-1.768%3CZ%3C0.364%29%20%3D%20P%28Z%3C0.364%29-P%28Z%3C-1.768%29%20%3D%200.642-0.0385%20%3D%200.604)
Step-by-step explanation:
a. If we select a random sample of 50 households, what is the standard error of the mean?
Previous concepts
Normal distribution, is a "probability distribution that is symmetric about the mean, showing that data near the mean are more frequent in occurrence than data far from the mean".
The Z-score is "a numerical measurement used in statistics of a value's relationship to the mean (average) of a group of values, measured in terms of standard deviations from the mean".
Let X the random variable that represent the amount of life insurance of a population, and for this case we know the distribution for X is given by:
Where
and
If we select a sample size of n =35 the standard error is given by:
![\sigma_{\bar X} = \frac{\sigma}{\sqrt{n}}= \frac{40000}{\sqrt{50}}= 5656.85](https://tex.z-dn.net/?f=%20%5Csigma_%7B%5Cbar%20X%7D%20%3D%20%5Cfrac%7B%5Csigma%7D%7B%5Csqrt%7Bn%7D%7D%3D%20%5Cfrac%7B40000%7D%7B%5Csqrt%7B50%7D%7D%3D%205656.85)
b. What is the expected shape of the distribution of the sample mean?
Since the distribution for X is normal then we know that the distribution for the sample mean
is given by:
c. What is the likelihood of selecting a sample with a mean of at least $112,000?
For this case we want this probability:
![P(X > 112000)](https://tex.z-dn.net/?f=%20P%28X%20%3E%20112000%29)
And we can use the z score given by:
![z= \frac{\bar X -\mu}{\frac{\sigma}{\sqrt{n}}}](https://tex.z-dn.net/?f=%20z%3D%20%5Cfrac%7B%5Cbar%20X%20%20-%5Cmu%7D%7B%5Cfrac%7B%5Csigma%7D%7B%5Csqrt%7Bn%7D%7D%7D)
And replacing we got:
![P( \bar X >112000) = P(Z>\frac{112000-110000}{\frac{40000}{\sqrt{50}}}) = P(Z>0.354)](https://tex.z-dn.net/?f=%20P%28%20%5Cbar%20X%20%3E112000%29%20%3D%20P%28Z%3E%5Cfrac%7B112000-110000%7D%7B%5Cfrac%7B40000%7D%7B%5Csqrt%7B50%7D%7D%7D%29%20%3D%20P%28Z%3E0.354%29)
And we can use the complement rule and we got:
![P(Z>0.354) = 1-P(Z](https://tex.z-dn.net/?f=%20P%28Z%3E0.354%29%20%3D%201-P%28Z%3C0.354%29%20%3D%201-0.600%20%3D%200.400)
d. What is the likelihood of selecting a sample with a mean of more than $100,000?
For this case we want this probability:
![P(X > 100000)](https://tex.z-dn.net/?f=%20P%28X%20%3E%20100000%29)
And we can use the z score given by:
![z= \frac{\bar X -\mu}{\frac{\sigma}{\sqrt{n}}}](https://tex.z-dn.net/?f=%20z%3D%20%5Cfrac%7B%5Cbar%20X%20%20-%5Cmu%7D%7B%5Cfrac%7B%5Csigma%7D%7B%5Csqrt%7Bn%7D%7D%7D)
And replacing we got:
![P( \bar X >100000) = P(Z>\frac{100000-110000}{\frac{40000}{\sqrt{50}}}) = P(Z>-1.768)](https://tex.z-dn.net/?f=%20P%28%20%5Cbar%20X%20%3E100000%29%20%3D%20P%28Z%3E%5Cfrac%7B100000-110000%7D%7B%5Cfrac%7B40000%7D%7B%5Csqrt%7B50%7D%7D%7D%29%20%3D%20P%28Z%3E-1.768%29)
And we can use the complement rule and we got:
![P(Z>-1.768) = 1-P(Z](https://tex.z-dn.net/?f=%20P%28Z%3E-1.768%29%20%3D%201-P%28Z%3C-1.768%29%20%3D%201-0.0385%20%3D%200.962)
e. Find the likelihood of selecting a sample with a mean of more than $100,000 but less than $112,000
For this case we want this probability:
![P(100000](https://tex.z-dn.net/?f=%20P%28100000%3CX%20%3C%20112000%29)
And we can use the z score given by:
![z= \frac{\bar X -\mu}{\frac{\sigma}{\sqrt{n}}}](https://tex.z-dn.net/?f=%20z%3D%20%5Cfrac%7B%5Cbar%20X%20%20-%5Cmu%7D%7B%5Cfrac%7B%5Csigma%7D%7B%5Csqrt%7Bn%7D%7D%7D)
And replacing we got:
![P(100000< \bar X](https://tex.z-dn.net/?f=%20P%28100000%3C%20%5Cbar%20X%20%3C112000%29%20%3D%20P%28%3C%5Cfrac%7B100000-110000%7D%7B%5Cfrac%7B40000%7D%7B%5Csqrt%7B50%7D%7D%7D%3CZ%3C%5Cfrac%7B112000-110000%7D%7B%5Cfrac%7B40000%7D%7B%5Csqrt%7B50%7D%7D%7D%29%20%3D%20P%28-1.768%3CZ%3C0.364%29)
And we can use the complement rule and we got:
![P(-1.768](https://tex.z-dn.net/?f=%20P%28-1.768%3CZ%3C0.364%29%20%3D%20P%28Z%3C0.364%29-P%28Z%3C-1.768%29%20%3D%200.642-0.0385%20%3D%200.604)