SOLUTION: How do I determine the correct critical value (s) in each of the following situations A two-tailed test with alpha = 0.025. Assume the value of the population standard deviatio

Question 266178: How do I determine the correct critical value (s) in each of the following situations
A two-tailed test with alpha = 0.025. Assume the value of the population standard deviation is known.
A left-tailed test with alpha = 0.10, unknown population standard deviation, and a sample size of 35.
I know that the data is normally distributed, I have tried working backwards from the sample size but I can't seem to get past the unknow population standard deviation. What am I doing wrong?

Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
How do I determine the correct critical value (s) in each of the following situations
A two-tailed test with alpha = 0.025. Assume the value of the population standard deviation is known.
Some text's say you should use the z-distribution when sigma is known.
But the more modern approach is to always use the t-distribution when
testing population means.
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A left-tailed test with alpha = 0.10, unknown population standard deviation, and a sample size of 35.
Again, the older texts say use the z-dist if n > 30.
But newer texts say us the t-dist of tests of population means.
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I know that the data is normally distributed, I have tried working backwards from the sample size but I can't seem to get past the unknow population standard deviation. What am I doing wrong?
You're not doing anything wrong.
If your text is old you get one answer.
If the text is more up to date you get different answers.
Cheers,
Stan H.

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