Acoin-operated drink machine was designed to discharge a mean of 6 ounces of coffee per cup. in a test of the machine, the discharge amounts in 20 randomly chosen cups of coffee from the machine were recorded. the sample mean and sample standard deviation were 6.13 ounces and 0.23 ounces, respectively. if we assume that the discharge amounts are normally distributed, is there enough evidence, at the 0.05 level of significance, to conclude that the true mean discharge, differs from 6 ounces?