The ages of registered voters in Smith County are normally distributed with a population standard deviation of 3 years and an unknown population mean. A random sample of 18 voters is taken and results in a sample mean of 55 years. Find the margin of error for a 95% confidence interval for the population mean. 20.01 20.10 1.282 20.05 1.645 20.025 1.960 20.005 2.576 2.326 You may use a calculator or the common z values above. • Round the final answer to two decimal places.

The margin of of error for a 95% confidence interval for the population mean is of 1.39 years.

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 = 1.96.

The margin of error is:

In which is the standard deviation of the population and n is the size of the sample.

Population standard deviation of 3 years

This means that

Sample of 18 voters

This means that

Margin of error:

The margin of of error for a 95% confidence interval for the population mean is of 1.39 years.

part A:

company a

30m+15

m= matress

company b

28m+21

m=matresses sold

part B:

company a

30(6)+15

195$

company b

28(6)+21

189$

company B charges less

part C:

company a

30(3)+15

105$

company b

28(3)+21

105$

there is no change at all so you do not save anything.