Question

Bongo’s nut bar is produced at a highly automated facility.  One of the quality control factors is the weight of each bar.  Samples of 10 bars are taken regularly and adjustments are made based on the outcome of quality control process.  Average weights and ranges of the latest samples are reported as following:

Sample	Average weight (gram)	Range
1	51	5
2	53	4
3	48	1
4	49	3
5	52	2

1. What is the upper control limit of X chart?
   1. 50.5
   2. 51.1
   3. 51.5
   4. 52.3
2. What is the lower control limit of R chart?
   1. 0.67
   2. 0.74
   3. 0.81
   4. Not computable
3. What is the status of production process based on this report?
   1. Both R and X charts indicate that the process is out of statistical control
   2. R chart indicates that process is out of statistical control but not X chart
   3. X chart indicates that process is out of statistical control but not R chart
   4. Both R and X charts indicate that the process is in statistical control

Answer 1

sample	average	range
1	51	5
2	53	4
3	48	1
4	49	3
5	52	2
average	50.6	3

1)

sample mean x̅ =			50.6
average range R̅ =			3
sample size n   =			10
for sample size n=10, criitcal value of constant A2=					0.308

upper control limit =x̅+3*A2R̅ =

51.5240

option C

2)

sample size n   =			10
for sample size n=4, criitcal value of constant D3=					01.777

lower control limit(LCL) =D3R̅ =

0.67

option A

3)

X chart indicates that process is out of statistical control but not R chart