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Bcom 447: Statistical Quality Control Question Paper
Bcom 447: Statistical Quality Control
Course:Bachelor Of Commerce
Institution: Chuka University question papers
Exam Year:2013
CHUKA
UNIVERSITY
UNIVERSITY EXAMINATIONS
FOURTH YEAR EXAMINATION FOR THE AWARD OF DEGREE OF
BACHELOR OF COMMERCE
BCOM 447: STATISTICAL QUALITY CONTROL
STREAMS: BCOM Y4S1 TIME: 2 HOURS
DAY/DATE:
INSTRUCTIONS:
Answer question one and any other two questions.
Do not write on the question paper.
Question ONE (30 Marks)
Give brief description of the following terms as used in quality control. [8 marks]
Acceptance quality level (AQL)
Lot tolerance percentage defective (LTPD)
Variables
Attributes
Briefly explain three tools of statistical control. [6 marks]
(i) A drilling machine bores holes with a mean diameter of 0.5230 cm and a standard
deviation of 0.0032 cm. Calculate the 2s and 3s upper and lower control limits for means of sample of four and prepare a control sheet. [7 marks]
(ii) Under what circumstances is standard deviation chart most ideal in statistical quality control? [3 marks]
During an examination of equal length of cloth, the following number of defects were observed 2, 3, 4, 0, 5, 6, 7, 4, 3, 2
Draw a control chart for the number of defects and comment whether the process is under control or not. [6 marks]
Question TWO (20 Marks)
Briefly explain six characteristics of a quality control officer. [6 marks]
A machine is set to deliver packets of a given weight. 10 samples of size 5 were recorded. Below are given relevant data:
Sample No: 1 2 3 4 5 6 7 8 9 10
Mean (X): 15 17 15 18 17 14 18 15 17 16
Range (R): 7 7 4 9 8 7 12 4 11 5
Calculate the values for the central line and the control limits for mean chart and then comment on the state of control (conversion Factors for n=5, are A2 = 0.58, D3 = 0,
D4 = 2.11). [10 marks]
Using the results (i) show the limits in an appropriate chart. [4 marks]
Question THREE (20 Marks)
Samples of 100 bottle tops were drawn randomly from the output of a process that produces several thousand units daily. Sample items were inspected for quality and defective ones were rejected. The result of a series of 20 samples is shown below.
Sample No No. Inspected No. Defectives Sample No No. Inspected No. Defectives
1 100 8 11 100 17
2 100 10 12 100 14
3 100 13 13 100 13
4 100 14 14 100 15
5 100 15 15 100 8
6 100 16 16 100 6
7 100 17 17 100 10
8 100 18 18 100 7
9 100 19 19 100 4
10 100 20 20 100 10
Determine the upper and lower control limit of the process and commend on your findings.
Question FOUR (20 Marks)
Explain the terms “chance variation” and “assignable variation” a suitable examples. [4marks]
Distinguish the following terms as used in quality control
Producer’s risk and consumer’s risk
Single sampling and double sampling plans
Process control and product control
Control limits and tolerance limits [16 marks]
Question FIVE (20 Marks)
(i) Write short notes on ‘OC’ curve.
Draw OC curve for the following single sampling plan
N = 50, n = 10 and C = 1 [8 marks]
State and explain three advantages of a cumulative sum (CUSUM) charts over Shewhart charts. [6 marks]
State and explain three advantages of sampling over 100% count. [6 marks]
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