Is there a difference in the satisfaction rating of traditional cellphone providers who bill for service at the end of a month often under a contract and prepaid cellphone service providers who bill in advance without a contract? The file CellphoneProviders contains the satisfaction rating for 10 traditional cellphone providers and 13 prepaid cellphone service providers.

Source: Data extracted from “Carrier Ratings: Why It Pays to Think Small,” Consumer Reports, February 2016, p. 51.

a. Assuming that the population variances from both types of cellphone providers are equal, is there evidence of a difference in the mean ratings between the two types of cellphone providers? (Use α = 0.05.)

b. Find the p-value in (a) and interpret its meaning.

c. What other assumption is necessary in (a)?

d. Assuming that the population variances from both cellphone providers are equal, construct and interpret a 95% confidence interval estimate of the difference between the population means of the two cellphone providers.

e. What conclusions can you reach about the satisfaction rating of traditional cellphone providers who bill for service at the end of a month often under a contract and prepaid cellphone service providers who bill in advance without a contract?