Question

A group students collected data on the speed of vehicles traveling through a construction zone on a state highway, where the posted speed was 45 mph. The recorded speed (in mph) of 15 randomly selected vehicles is given below. You should be able to copy and paste them into Excel.

35
37
40
41
42
44
46
49
52
54
58
61
64
66
67

- Use Excel Data Analysis to find the mean, median, and mode of the data set. Make sure that you clearly state or point out which numbers are which. Don’t expect me to pick the numbers I want.

- Assuming speeds are approximately normally distributed, use Data Analysis to construct a 95% confidence interval for the true mean speed of drivers in this construction zone. Interpret the interval.

- Construct a 99% confidence interval for the true mean speed of drivers in this construction zone. Interpret the interval.

- Compare the widths of the 95% and 99% confidence intervals.

- What conclusions do you draw about the speeds people drive in this construction zone?

Answer 1

Discriptive Statistics
Mean	50.4
Standard Error	2.790801216
Median	49
Mode	#N/A
Standard Deviation	10.80872663
Sample Variance	116.8285714
Kurtosis	-1.349596941
Skewness	0.235636178
Range	32
Minimum	35
Maximum	67
Sum	756
Count	15
Confidence Level(95.0%)	5.985673297
Confidence Level(99.0%)	8.307776324

95% confidence interval is given by

99% confidence interval is given by

Compare the widths of 95% and 99% confidence intervals.

Range of 95% confidence interval = 71.58-29.21=42.37

Range of 99% confidence interval =78.246-22.55=55.69

What conclusions do you draw about the speeds people drive in this construction zone?

The conclusion is that the average speed is not 45 mph