Question

National Fuelsaver Corporation manufactures the Platinum Gasaver, a device they claim "may increase gas mileage by 30%." Here are the percent changes in gas mileage for 15 identical, randomly-selected vehicles, as presented in one of the company's advertisements: –2.4 6.9 10.4 10.8 24.8 28.7 28.7 33.7 34.6 38.5 40.2 44.6 46.8 46.9 48.3 (a) The sample mean is x−=29.43 and the sample standard deviation is s =16.23. Calculate and interpret the standard error of the mean for these data. (b) Construct and interpret a 90% confidence interval to estimate the mean change (in percent) in

Answer 1

what os your data? you said percentages but listed the sample mean (vs. the sample proportion).

-2.4?

Answer 2

Sample mean (xbar) = 29.43
–2.4 6.9 10.4 10.8 24.8
28.7 28.7 33.7 34.6 38.5
40.2 44.6 46.8 46.9 48.3

15 pieces of data

Answer 3

sorry, not a proportion problem.
which distribution are you using?

Answer 4

t distribution, but if the distribution is heavily skewed or has outliers, you can't use t.
This is the rest of part B:
(b) Construct and interpret a 90% confidence interval to estimate the mean change (in percent) in gas mileage. Does the data support the company's claim? Use the four-step process.

Answer 5

so what's the standard error of estimate?

Answer 6

I found it to be 4.191 (this is the answer to part A)

Answer 7

what's the critical t value?

Answer 8

It's 1.761 for 90% confidence and a t with 14 degrees of freedom