Question
Police on a heavily traveled highway claim that the average car exceeds the speed limit of...
Police on a heavily traveled highway claim that the average car exceeds the speed limit of 65 mph by more than 10 mph. A random sample of 50 cars is evaluated and found to have an average speed of 82.5 mph with a standard deviation for this sample of 7.3 mph. Determine the 95% confidence interval for this example, state the null and alternative hypothesis about the police’s claim and determine if the claim is indeed correct at a significance level of α=0.05 (5 points).
Homework Answers
Answer #1
Given : Sample size=n=50
Sample mean 
Sample standard deviation=s=7.3
Significance level=
Hypothesis: 
Vs 
Therefore , the 95% confidence interval for the true population mean is ,
Where , 
, The Excel function is , =TINV(0.05,49)
Decision : Here , the value 
does not lies in the 95% confidence interval
Therefore , reject Ho.
Conclusion : Hence , there is sufficient evidence to support the claim that the average car exceeds the speed limit of 65 mph by more than 10 mph.
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