The travel -to-work time for residents of the 15 largest cities in the united st

Question

The travel -to-work time for residents of the 15 largest cities in the united states is reported in the 2003 Information please Almanac. Suppose that preliminary single random sample of residents of San Francisco is used to develop a planning value of 6.00 minutes for the population standard deviation. If we want to estimate the population mean travel-to-work time for San Francisco residents with a margin of error of 2 minute, what sample size should be used? Assume 95% confidence. If we want to estimate the population mean travel-to-work time for San Francisco residents with a margin of error of 1 minute, what sample size should be used? Assume 95% confidence.

Explanation / Answer

n = (zc*s)^2/E^2

   zc is the critical value we find from normal table for 5% level of significance (100% - 95%).

zc = 1.96

E = 1

s= 6

n = (1.96*6)^2/1^2 = 138.3

If we take the nearest number then the answer is 138

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