Below you'll find the question and my attempt at some of the answers, which are probably way off.
Monthly profits (in million dollars) of two phone companies were collected from the past five years (60 months) and some statistics are given in the following table.
Company | Mean | SD
Rogers | 123.7|25.5
Bell | 242.7|15.4
(a) Find a point estimate for the difference in the average monthly profits of these two phone companies.
I subtracted the two means (242.7-123.7) and got 119.
(b) What is the margin of error for a 99% confidence interval for the difference in the average monthly profits of these two phone companies?
z = (1 - 0.99)/2 z = 0.01/2 z =0.005 1 - 0.005 = 0.995 p(z < 3.275) = 0.995
From looking online, I found this formula but I couldn't figure out how to fill in the values: ME = t(stdev/√n)
I don't know where to go from here. I know the formulas for the confidence intervals, but I don't understand what I'm supposed to do given that there are two standard devs and means? I don't know whether n is 60 or 2.
(c) Based on the constructed 99% confidence interval in part (b), can we conclude that there is a difference in the average monthly profits of these two phone companies?
(d) Given the level of significance α = 1%, test whether Bell's average monthly profit is more than Rogers'.