Question

The EPA tests vehicles for gasoline mileage under stringent testing conditions.

The testing for a particular make and model of mid-sized SUV involved 35 vehicles submitted by the manufacturer.

Assume the vehicles submitted for testing constitute a random sample from the population.

Construct a 99% confidence interval estimate for the estimated mean MPG mileage for the vehicle tested.

Make a statement to interpret your results.

MPG

26.1

24.6

24.7

25

25.3

25.5

25.8

25.9

26

26

26

26.1

26.2

26.2

26.3

26.4

26.4

26.4

26.5

26.5

26.6

26.6

26.7

27

27

27

27.1

27.1

27.3

27.4

27.4

27.5

27.5

27.8

27.9

How would I input this into excel 2016

Answer 1

First of all, copy and paste these 35 values in a one column of your 2016 excel sheet

Alpha level for this calculation is 1 - 0.99 = 0.01

then find mean, standard deviation using the following formulas

for mean, use =AVERAGE in a cell, select all the 35 values and you will get mean = 26.4618

for standard deviation, use =STDEVP in next cell, select all the 35 values and you will get stdev = 0.8214

and you have sample size n = 35

In next cell, type the formula CONFIDENCE(alpha, standard deviation, size)

put alpha = 0.01, standard deviation = 0.8214 and size = 35

you will get confidence = 0.3576

So, your confidence interval will be (26.4618-0.3576, 26.4618+0.3576) = (26.1042, 26.8194)

so, the required 99% confidence interval is (26.1042, 26.8194)

Interpreation

we are 99% confident that the estimated mean MPG mileage for the 35 vehicle tested fall within the range 26.1042 MPG to 26.8194 MPG