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Answer:
The 90% confidence interval for the true mean daily wage of all union workers in the industry is ($118.6, $125.4). The lower limit is $118.6 and the upper limit is $125.4.
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.
[tex]M = 1.645\frac{20}{\sqrt{90}} = 3.4[/tex]
The lower end of the interval is the sample mean subtracted by M. So it is 122 - 3.4 = $118.6
The upper end of the interval is the sample mean added to M. So it is 122 + 3.4 = $125.4
The 90% confidence interval for the true mean daily wage of all union workers in the industry is ($118.6, $125.4). The lower limit is $118.6 and the upper limit is $125.4.
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