7. when companies employ control charts to monitor the quality of their products, a series of small samples is typically used to determine if the process is “in control” during the period of time in which each sample is selected. suppose a concrete-block manufacturer samples nine blocks per hour and tests the breaking strength of each. during one-hour’s test, the mean and standard deviation are 985.6 pounds per square inch (psi) and 22.9 psi, respectively. a. construct a 99% confidence interval for the mean breaking strength of blocks produced