Question

1. A company manufactures an electrical cooling fan.  When the fans are performing properly, samples of 200 fans average 12.5 watts with an average range of 1.2 watts.  A 3σ control chart program is being used to monitor the performance of the fans, and these data from the 10 most recent samples were collected:

Sample Number	Sample Mean	Sample Range
1	12.5	1.1
2	12.45	1.2
3	12.55	0.9
4	12.50	0.8
5	12.45	0.9
6	12.60	1.0
7	12.48	1.4
8	12.46	1.1
9	12.56	0.9
10	12.48	0.8

1. Compute the 3σ control limits and center line for an ⁻x chart.
2. Compute the 3σ control limits and center line for an R chart.
3. Plot the sample data on the ⁻x and R charts and decide if the performance of the fan is in control.

Answer 1