Question 234356
I recommend you draw the picture of each of these so you can 
see the meaning of the problem and the answer.
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For a one-tailed test (lower tail), a sample size of 26 at 90% confidence, 
t = invT(0.10,25) = -1.3163
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For a one-tailed test (upper tail) at 87.7% confidence, 
Z = invNorm(0.877) = 1.1601
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In a two-tailed hypothesis test the test statistic is determined to be -2.5. The p-value for this test: 2P(z < -2.5) = 2*normalcdf(-100,-2.5) = 0.01242
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For a two-tailed test, a sample of 25 at 80% confidence, 
t = +/-invT(0.10,24) = +/-1.3178
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Cheers,
Stan H.