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2 answers:
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Answer:
a. Assume that the population has a normal distribution.
b. The 90% confidence interval of the mean sale time for all homes in the neighborhood is between 219.31 days and 240.69 days.
Step-by-step explanation:
Question a:
We have to assume normality.
Question b:
We have that to find our level, that is the subtraction of 1 by the confidence interval divided by 2. So:
Now, we have to find z in the Ztable as such z has a pvalue of .
That is z with a pvalue of , so Z = 1.645.
Now, find the margin of error M as such
In which is the standard deviation of the population and n is the size of the sample.
The lower end of the interval is the sample mean subtracted by M. So it is 230 - 10.69 = 219.31 days.
The upper end of the interval is the sample mean added to M. So it is 230 + 10.69 = 240.69 days.
The 90% confidence interval of the mean sale time for all homes in the neighborhood is between 219.31 days and 240.69 days.