A doctor at a local hospital is interested in estimating the birth weight of infants. How large a sample must she select if she desires to be 90% confident that her estimate is within 4 ounces of the true mean

The minimum sample size needed is . If n is a decimal number, it is rounded up to the next integer. is the standard deviation of the population.

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 = 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.

How large a sample must she select if she desires to be 90% confident that her estimate is within 4 ounces of the true mean?

A sample of n is needed, and n is found when M = 4. So

The minimum sample size needed is . If n is a decimal number, it is rounded up to the next integer. is the standard deviation of the population.

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step-by-step explanation: