It has been shown that people drive 5 - 10mph faster than the posted speed limit on a highway. It has been thought that changing the speed limit from 65mph to 70mph would not increase the "typical" speed of 70 - 75mph. On one stretch of a highway the speed limit was increase from 65mph to 70mph. If the population mean speed on this stretch of the highway has been 68mph with a standard deviation of 5mph, what is the sample size needed to detect an increase in speed on this stretch of the highway of 10mph? Let ? = 0.02 and ? = 0.05
Write the null and alternative hypotheses:
Draw the curves and label ? and ?:
Calculate the sample size: