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Answer:
The 95 percent confidence interval for the average number of strokes is (3.858, 3.642).
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 Ztable as such z has a pvalue of .
So it is z with a pvalue of , so
Now, find 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 mean subtracted by M. So it is 4.25 - 0.392 = 3.858
The upper end of the interval is the mean added to M. So it is 4.25 + 0.392 = 4.642
The 95 percent confidence interval for the average number of strokes is (3.858, 3.642).