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Hypothesis Testing: One-tailed and Two-tailed Testing

I've been trying to understand the differences between one tailed and two tailed testing, t and z testing and p value. I think I understood #5 but need some help with #18, 23 and 44.

18. The management of White Industries is considering a new method of assembling its golf cart. The present method requires 42.3 minutes, on the average, to assemble a cart. The mean assembly time for a random sample of 24 carts, using the new method, was 40.6 minutes, and the standard deviation of the sample was 2.7 minutes. Using the .10 level of significance, can we conclude that the assembly time using the new method is faster?

23. Experience raising New Jersey Red chickens revealed the mean weight of the chickens at five months is 4.35 pounds. The weights follow the normal distribution. In an effort to increase their weight, a special additive is added to the chicken feed. The subsequent weights of a sample of five-month-old chickens were (in pounds):

4.41 4.37 4.33 4.35 4.30 4.39 4.36 4.38 4.40 4.39

At the .01 level, has the special additive increased the mean weight of the chickens? Estimate the p-value.

44. A recent article in the Wall Street Journal reported that the 30-year mortgage rate is now less than 6 percent. A sample of eight small banks in the Midwest revealed the following 30-year rates (in percent):

4.8 5.3 6.5 4.8 6.1 5.8 6.2 5.6

At the .01 significance level, can we conclude that the 30-year mortgage rate for small banks is less than 6
percent? Estimate the p-value.

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This solution provides calculations in Excel for the differences between one-tailed and two-tailed testing.

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