Suppose I surveyed a random sample of commuters who had jobs in Manhattan, 51 whose primary mode of transportation was bus (B) or subway (S) and 80 whose primary mode was Metro-North (MN) or the Long Island Railroad (LIRR). Of the 51 in the first group, the mean annual income was $40,000 with a standard deviation of $5,100; of the 80 in the latter group, the mean annual income was $60,000 with a standard deviation of $8,000. (a) The question of interest
Suppose I surveyed a random sample of commuters who had jobs in Manhattan, 51 whose primary
(a) The question of interest is whether the mean income levels of the two populations of commuters are different. State the null hypothesis in words, or in mathematical form.
(b) What is the critical t at the 95% confidence level (to 3 decimal places)?
(b) Please give a 95% confidence interval for the difference in mean income levels of the two groups (to the nearest dollar).
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