Source: $1950$ ASTM Manual on Quality Control of Materials, copyright American Society for Testing Materials. Reprinted with permission.

Historically, the average time to service a customer complaint has been $3$ days and the standard deviation has been $0\mathrm{.}50$ day. Management would like to specify the control limits for an chart with a sample size of $10$ and $3-$ sigma limits$.$ The UCL for the chart would be:

less than or equal to $3\mathrm{.}30.$

greater than $3\mathrm{.}30$ but less than or equal to $3\mathrm{.}40.$

greater than $3\mathrm{.}40$ but less than or equal to $3\mathrm{.}50.$

greater than $3\mathrm{.}50.$