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Thu 21 Feb, 2013 08:17 am
Good Morning,
I am taking a business statistics course and I can't seem to figure out how to find the missing figures in the following problem, and I came across your website and thought it wouldn't hurt to ask!
Here's the question:
Using the data below, determine the trial central line and trial control limits for the Xbar chart. Subgroup size is 5. For the R chart, the trial central line is 0.11, the UCL is 0.23, and LCL is 0. Note not all of the subgroups are included in the data; however, the sums are correct.
Subgroup X-Bar R
1 2.08 .05
2 2.09 .24
3 2.08 .10
* * *
* * *
* * *
25 2.09 .11
=52.0 =2.75
Any information you could provide would be wonderful.
Thank you,
Natalie Gainey
@ngainey,
You can find the trial central line for the X-bar chart by taking the mean of the means of the subgroups. You are given that the sum of the subgroups is 52.0 and you have 25 subgroups. The mean of the means (sometimes called X-double bar) is 52.0/25. The upper and lower control limits for the X-bar chart use the values given to you for the R chart. The UCL for the Xbar = X-double bar + A2*Rbar and the LCL is X-double bar - A2*Rbar. You are given Rbar=0.11. You'll need the value of A2 for a subgroup size = 5 (use 0.577 if you don't have an A2 value table available).
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