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You are planning a survey of starting salaries for recent computer science majors. In the latest survey by the National Association of Colleges and Employers, the average starting salary was reported to be $60,038. 5 If you assume that the standard deviation is $4300, what sample size do you need to have a margin of error equal to $500 with 95% confidence

Sagot :

Answer:

A sample size of 285 is needed.

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 - 0.95}{2} = 0.025[/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 - 0.025 = 0.975[/tex], so Z = 1.96.

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.

Standard deviation is $4300

This means that [tex]\sigma = 4300[/tex]

What sample size do you need to have a margin of error equal to $500 with 95% confidence?

A sample size of n is needed. n is found when M = 500. So

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

[tex]500 = 1.96\frac{4300}{\sqrt{n}}[/tex]

[tex]500\sqrt{n} = 1.96*4300[/tex]

[tex]\sqrt{n} = \frac{1.96*4300}{500}[/tex]

[tex]n = 284.1[/tex]

Rounding up

A sample size of 285 is needed.