Historically, the average time to service a customer complaint has been 3 days and the standard deviation has been 0.50 day. Management would like to specify the control limits for an X- chart with a sample size of 10 and 3 sigma limits. The UCL for the chart would be ---
A) less than or equal to 3.30.
B) greater than 3.30 but less than or equal to 3.40.
C) greater than 3.40 but less than or equal to 3.50.
D) greater than 3.50.

Question

Quizplus · Accepted Answer

The UCL (Upper Control Limit) for an X-chart is calculated as the average plus 3 times the standard error. The standard error is the standard deviation divided by the square root of the sample size. Here, UCL = 3 + 3*(0.50/√10) = 3 + 0.474 = 3.474, which falls in the range greater than 3.40 but less than or equal to 3.50.

Historically, the Average Time to Service a Customer Complaint Has