6.3. The time to make beds at a motel should fall into an agreed-on range of times. A sample of four housekeeping people was selected, and the time needed to make a bed was observed on three different days:

a. Determine the upper and lower control limits for an¯X-chart and an R-chart with a sample size of four.

b. After the control chart was established, a sample of four observations had the following times in seconds: 185, 150, 192, and 178. Is corrective action needed?