Confidence Intervals 1) You are suspicious that vehicles are speeding excessivel

Question

Confidence Intervals

1) You are suspicious that vehicles are speeding excessively on Maple Street, a 30 mph road in your neighborhood and you need some data to take to the mayor of your city regarding your suspicion. No data is available for speeds on this street. You decide to take a sample of speeds and bring the results to the mayor. The speeds of the vehicles you sampled were as follows (you can assume a normal distribution):

29 35 38 26 40 37 50 41 34 36 29 36 32 39 43 41 34 39 44 35 33 28 47

a)

You figure that you need to be 95% confident in your findings to the mayor. What is the interval you believe the average speed of all the vehicles (population) traveling on this road is? Please make sure you provide an accurate and thorough interpretation for full credit.

b)

The mayor claims that the interval you provided to him was too wide and he determined it was inconclusive. You still need to be 95% confident so you decided to take more vehicle samples to tighten up your interval. The remaining speed samples you recorded were as follows:

31 37 34 36 29 27 26 33 29 36 39 32 31 40 40 28 35 35 31 42 26

What is the revised interval you believe the average speed of all vehicles (population) is based on the original samples you took plus the additional samples you took (combine to one dataset)? Please make sure you provide an accurate and thorough interpretation for full credit.

c)

When you returned to the Mayor’s office, do you think the mayor was satisfied with the revised interval? Provide a brief paragraph on the analysis of results based on your findings in a versus your findings in b.

Note: This is an excel project. I want to know how to do it in Excel, not the solution only. Thank you

Explanation / Answer

1)

Enter all the data in Excel.

For sample mean use the command =AVERAGE (,) Select all the data

For Standard Error use the command : =CONFIDENC.NORM(0.05,STDEV(,),22)

CI = (Sample Average- SD, Sample Average + SD)

2)

3)

Length of the interval is less in B when compared to A.

SD of A is higher than SD of B

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