Control Limits Calculation and Standard Deviation Problems

Control Limits Calculation and Standard Deviation Problems

A company that makes car accessories. The company control its production process by periodically taking a sample of 99 units from the production line. Each product is inspected for defective features. Control limits are developed using three standard deviations from the mean as the limit. During the last 12 samples taken, the proportion of defective items per sample was recorded as follows:

0.01 0.03 0.0 0.04 0.01 0.01
0.00 0.01 0.02 0.02 0.03 0.03

a. Determine the mean proportion defective, the UCL, and the LCL? (Marks 1) (word count maximum:150)

b. Draw a control chart and plot each of the sample measurements on it? (Marks 1) (word count maximum:100)

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c. Does it appear that the process for making tees is in statistical control? (Marks 0.5) (word count maximum:100)

Question 2:

A Chemical Company estimates the annual demand for a certain product as follows:

Week 1 2 3 4 5 6
Demand 649 524 561 738 511 600
  • Forecast the demand for week 7 using a five-period moving average? (Marks 0.5) (word count maximum:100)
  • Forecast the demand for week 7 using a three-period weighted moving average. Use the following weights: W1 = .5, W2 = .3, W3 = .2.? (Marks 0.5) (word count maximum:100)
  • Forecast the demand for week 7 using exponential smoothing. Use an α value of .1 and assume the forecast for week 6 was 602 units? (Marks 1) (word count maximum:100)
  • What assumptions are made in each of the above forecasts? (Marks 0.5) (word count maximum:150)