Bob Nale is the owner of Nales Quick Fill Bob would like to

Bob Nale is the owner of Nale\'s Quick Fill. Bob would like to estimate the mean number of gallons of gasoline sold to his customers. Assume the number of gallons sold follows the normal distribution with a population standard deviation of 2.3 gallons. From his records, he selects a random sample of 59 sales and finds the mean number of gallons sold is 8.44. (Round your answers to 2 decimal places.)

The 90 percent confidence interval for the population mean is between  and .

Solution

Mean = 8.44

For 90% confidence, z = 1.645

Upper limit = Mean   + z * SD
UL = 8.44 + 1.645*2.3
UL = 12.2235

Lower limit = Mean - z*SD
LL = 8.44 - 1.645*2.3
LL = 4.6565

So, 4.66 to 12.22