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We are formulating a 90% confidence interval for the population mean and would like our confidence interval to have a margin of error that is not larger than 3. Experience suggests that a reasonable estimate for the population standard deviation is 15. What minimum sample size should be anticipate using? (NOTE: Round your final answer up to the next whole number).

Sagot :

Answer:

A sample size of 68 should be anticipated using.

Step-by-step explanation:

We have that to find our [tex]\alpha[/tex] level, that is the subtraction of 1 by the confidence interval divided by 2. So:

[tex]\alpha = \frac{1 - 0.9}{2} = 0.05[/tex]

Now, we have to find z in the Ztable as such z has a pvalue of [tex]1 - \alpha[/tex].

That is z with a pvalue of [tex]1 - 0.05 = 0.95[/tex], so Z = 1.645.

Now, find the margin of error M as such

[tex]M = z\frac{\sigma}{\sqrt{n}}[/tex]

In which [tex]\sigma[/tex] is the standard deviation of the population and n is the size of the sample.

Experience suggests that a reasonable estimate for the population standard deviation is 15

This means that [tex]\sigma = 15[/tex]

What minimum sample size should be anticipate using?

Margin of error at most 3, which means that the sample size is n when M = 3. So

[tex]M = z\frac{\sigma}{\sqrt{n}}[/tex]

[tex]3 = 1.645\frac{15}{\sqrt{n}}[/tex]

[tex]3\sqrt{n} = 1.645*15[/tex]

Simplifying both sides by 3:

[tex]\sqrt{n} = 1.645*5[/tex]

[tex](\sqrt{n})^2 = (1.645*5)^2[/tex]

[tex]n = 67.7[/tex]

Rounding up

A sample size of 68 should be anticipated using.