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Answer:
The 85% confidence interval for the mean number of toys purchased each year is (6.7, 6.9).
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 .
That is z with a pvalue of , so Z = 1.44.
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 6.8 - 0.1 = 6.7
The upper end of the interval is the sample mean added to M. So it is 6.8 + 0.1 = 6.9
The 85% confidence interval for the mean number of toys purchased each year is (6.7, 6.9).