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 random sample of n1 = 20 winter days in Denver gave a sample mean pollution index x1 = 43

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 random sample of n1 = 20 winter days in Denver gave a sample mean

pollution index x1 = 43. Previous studies show that σ1 = 18. For Englewood (a suburb of Denver), a random sample of n2 = 18 winter days gave a sample mean pollution index of x2 = 52. Previous studies show that σ2 = 15. Assume the pollution index is normally distributed in both Englewood and Denver. Do these data indicate that the mean population pollution index of Englewood is different (either way) from that of Denver in the winter? Use a 1% level of significance.
(a) What is the level of significance?
 




State the null and alternate hypotheses.
H0: μ1 = μ2; H1: μ1 ≠ μ2
H0: μ1 < μ2; H1: μ1 = μ2    
H0: μ1 = μ2; H1: μ1 < μ2
H0: μ1 = μ2; H1: μ1 > μ2




(b) What sampling distribution will you use? What assumptions are you making?
The Student's t. We assume that both population distributions are approximately normal with unknown standard deviations.
The standard normal. We assume that both population distributions are approximately normal with unknown standard deviations.    
The Student's t. We assume that both population distributions are approximately normal with known standard deviations.
The standard normal. We assume that both population distributions are approximately normal with known standard deviations.


What is the value of the sample test statistic? (Test the difference μ1 − μ2. Round your answer to two decimal places.)




(c) Find (or estimate) the P-value. (Round your answer to four decimal places.)