Our environment is very sensitive to the amount of ozone in the upper atmosphere

Question

Our environment is very sensitive to the amount of ozone in the upper atmosphere. The level of ozone normally found is 7.2 parts/million (ppm). A researcher believes that the current ozone level is not at a normal level. The mean of 25 samples is 6.9 ppm with a standard deviation of 0.6. Assume the population is normally distributed. A level of significance of 0.05 will be used. Make the decision to reject or fail to reject the null hypothesis. Reject Null Hypothesis Fail to Reject Null Hypothesis

Explanation / Answer

Mean = 6.9
Stdev = .6
Pop.mean = 7.2

t = (6.9-7.2)/(.6/sqrt(25)) = -2.5
df = n - 1 = 25-1 = 24

So, -2.064 is the critical value. Since -2.5<-2.064 we reject null hypothesis

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