9.11 A manufacturer of cereals claims that the contents of boxes sold weigh on average at least 20 ounces. The distribution of weight is known to be normal, with a standard deviation of 0.5 ounce. A random sample of 25 boxes yielded a sample mean weight of 19.96 ounces.

Test at the 10% significance level the null hypothesis that the population mean weight is at least 20 ounces.