A hotel tracks the number of complaints per month. When the process is in control, there is an average of 35 complaints per month. Assume that a 2-sigma control limit is used. What is the lower control limit?
A) less than or equal to 15
B) more than 15 but less than or equal to 20
C) more than 20 but less than or equal to 25
D) more than 25

Question

Quizplus · Accepted Answer

The lower control limit (LCL) is calculated as the average minus 2 times the standard deviation. Assuming a Poisson distribution, the standard deviation is the square root of the average (35). Thus, LCL = 35 - 2*sqrt(35) ≈ 35 - 11.83 ≈ 23.17, which falls in the range of more than 20 but less than or equal to 25.

A Hotel Tracks the Number of Complaints Per Month