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Answer:
A sample of 17 must be selected.
Step-by-step explanation:
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 Z-table as such z has a p-value of .
That is z with a pvalue of , so Z = 2.054.
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 standard deviation from a previous study is 4 hours.
This means that
How large a sample must be selected if he wants to be 96% confident of finding whether the true mean differs from the sample mean by 2 hours?
A sample of n is required.
n is found for M = 2. So
Simplifying both sides by 2:
Rounding up:
A sample of 17 must be selected.