An ad agency tracks the complaints, by week received, about the bllboards in its

Question

An ad agency tracks the complaints, by week received, about the bllboards in its city: Week No. of Complaints 4 17 10 This exercise contains only parts a, b, and c. a) The type of control chart that is best to monitor this process is c chart b) Using z = 3, the control chart limits for this process are (assume that the historical complaints rate is unknown UCLc15.72 complaints per week (round your response to two decimal places) LCLe*complaints per week (round your response to two decimal places and if your answer 1s negative, enter this value as 0) c) According to the control limits, the process has been OUT OF CONTROL

Explanation / Answer

a) The type of cintrol chart that is best to monitor this process is C-chart. Because here the number of complaints per unit of time is given.

b) Number of weeks = 6

Sum of complaints = 3+6+3+17+6+10 = 45

C-bar = Sum of complaints /number of weeks = 45/6 = 7.5

Using Z = 3,

UCLc = C-bar + (Z x sqrt of C-bar)

= 7.5 + (3 x sqrt of 7.5)

= 7.5 + (3 x 2.74)

= 7.5 + 8.22

= 15.72

LCLc = C-bar - (3 x sqrt of C-bar)

= 7.5 - (3 x sqrt of 7.5)

= 7.5 - (3 x 2.74)

= 7.5 - 8.22

= - 0.72

= 0 (when the value is negative it is taken as 0)

C) The process has been out of control as the number of complaints for week 4 is beyond the upper specification limit.

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