Question

One enterprising engineering student decided to test the whether or not changing his brand of gasoline would make a change in the gas mileage that he got from his car. Instead of buying B. P. gasoline, which gave him an average of 28 MPG on the highway, he decided to switch to a cheaper brand down the street. After driving home and filling up 35 times, he had collected enough data to determine that the sample average highway MPG was 25.2 with a standard deviation of 2.2. With a 0.05 significance level, do you or do not reject the null hypothesis

Answer 1

Solution :

This is the left tailed test .

The null and alternative hypothesis is ,

H₀ :   = 28

H_a : <  28

Test statistic = z

= ( - ) / / n

= (25.2 - 28) / 2.5 / 35

= -6.63

Test statistic = -6.63

P(z < -6.63) = 0

P-value = 0

= 0.05

P-value <

Reject the null hypothesis .