cell phone company offers two plans to its subscribers. At the time new subscribers sign up, they are asked to provide some demographic information. The mean yearly income for a sample of 45 subscribers to Plan A is $51,900 with a standard deviation of $9,000. For a sample of 20 subscribers to Plan B, the mean income is $54,000 with a standard deviation of $6,500.
At the 0.025 significance level, is it reasonable to conclude the mean income of those selecting Plan B is larger? Hint: For the calculations, assume the Plan A as the first sample.
The test statistic is