Instruction 18-10
a Supplier of Silicone Sheets for Producers of Computer

Instruction 18-10
A supplier of silicone sheets for producers of computer chips wants to evaluate her manufacturing process. She takes a sample size of five from each day's output and counts the number of blemishes on each silicone sheet. The results from 20 days of such evaluations are presented below. She also decides that the upper specification limit is 10 blemishes.
$\begin{array}{llllllll}\text{Day}&1&2&3&4&5&\text{Mean}&\text{Range}\\\hline1 & 8 & 10 & 14 & 6 & 5 & 8.6 & 9 \\2 & 8 & 13 & 6 & 6 & 10 & 8.6 & 7 \\3 & 10 & 12 & 7 & 7 & 9 & 9.0 & 5 \\4 & 5 & 9 & 12 & 7 & 10 & 8.6 & 7 \\5 & 8 & 3 & 8 & 9 & 10 & 7.6 & 7 \\6 & 9 & 7 & 9 & 6 & 9 & 8.0 & 3 \\7 & 10 & 10 & 5 & 7 & 6 & 7.6 & 5 \\8 & 10 & 9 & 10 & 6 & 5 & 8.0 & 5 \\9 & 6 & 10 & 6 & 9 & 9 & 8.0 & 4 \\10 & 6 & 9 & 8 & 6 & 8 & 7.4 & 3 \\11 & 8 & 5 & 6 & 10 & 10 & 7.8 & 5 \\12 & 6 & 4 & 7 & 7 & 12 & 7.2 & 8 \\13 & 7 & 5 & 7 & 6 & 9 & 6.8 & 4 \\14 & 5 & 8 & 8 & 7 & 6 & 6.8 & 3 \\15 & 7 & 12 & 10 & 6 & 10 & 9.0 & 6 \\16 & 7 & 11 & 4 & 7 & 8 & 7.4 & 7 \\17 & 8 & 4 & 5 & 4 & 7 & 5.6 & 4 \\18 & 11 & 4 & 11 & 11 & 10 & 9.4 & 7 \\19 & 6 & 10 & 6 & 10 & 10 & 8.4 & 4 \\20 & 6 & 12 & 12 & 6 & 8 & 8.8 & 6\end{array}$

-Referring to Instruction 18-10,an R chart is to be constructed for the number of blemishes.The centre line of this R chart is located at _______.