3.

(a)

Control chart is a graphical presentation of process data over time.

Explain the purpose of the following control charts, with one example for each chart.

i) Mean chart ii) Range chart iii) p-chart iv) c-chart

(b)

Assignable variation is defined as variation in a production process that ca be traced to specific causes.

List two possible causes of assignable variation.

(c)

The time needed for checking in at a hotel is to be investigated. Historically, the process has had a standard deviation equal to 0.146. The means of 26 samples of n=14 are shown below.

Sample	Mean		Sample	Mean
1	3.86		14	3.81
2	3.90		15	3.83
3	3.83		16	3.86
4	3.81		17	3.82
5	3.84		18	3.86
6	3.83		19	3.84
7	3.87		20	3.87
8	3.88		21	3.84
9	3.84		22	3.92
10	3.80		23	3.89
11	3.88		24	3.86
12	3.86		25	3.88
13	3.88		26	3.90
		Overall Mean =		3.856

1. Construct an appropriate control chart for this process with three-sigma limits.

2. Plot the information and look for points and patterns. What can you conclude?