49. Egyptian researchers, Kamal et al. (1991), took a sample of 126 police officers subject to inhalation of vehicle exhaust in downtown Cairo and found an average blood level concentration of lead...

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Extracted text: 49. Egyptian researchers, Kamal et al. (1991), took a sample of 126 police officers subject to inhalation of vehicle exhaust in downtown Cairo and found an average blood level concentration of lead equal to 29.2 μg/dl with a standard deviation of 7.5 ug/dl. A sample of 50 policemen from a suburb, Abbasia, had an average concentration of 18.2 μg/dl and a standard deviation of 5.8 μg/dl. Form a confi- dence interval for the population difference and test the null hypothesis that there is no difference in the populations.