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Problem 10-4
Computer upgrades have a nominal time of 80 minutes. Samples of five observations each have been taken, and the results are as listed.
SAMPLE
1 2 3 4 5 6
79.2 80.5 79.6 78.9 80.5 79.7
78.8 78.7 79.6 79.4 79.6 80.6
80.0 81.0 80.4 79.7 80.4 80.5
78.4 80.4 80.3 79.4 80.8 80.0
81.0 80.1 80.8 80.6 78.8 81.1
Factors for three-sigma control limits for x¯x¯ and R charts
FACTORS FOR R CHARTS
Number of Observations in Subgroup,
n Factor for
x¯x¯ Chart,
A2 Lower
Control Limit,
D3 Upper
Control Limit,
D4
2 1.88 0 3.27
3 1.02 0 2.57
4 0.73 0 2.28
5 0.58 0 2.11
6 0.48 0 2.00
7 0.42 0.08 1.92
8 0.37 0.14 1.86
9 0.34 0.18 1.82
10 0.31 0.22 1.78
11 0.29 0.26 1.74
12 0.27 0.28 1.72
13 0.25 0.31 1.69
14 0.24 0.33 1.67
15 0.22 0.35 1.65
16 0.21 0.36 1.64
17 0.20 0.38 1.62
18 0.19 0.39 1.61
19 0.19 0.40 1.60
20 0.18 0.41 1.59

a. Using factors from above table, determine upper and lower control limits for mean and range charts. (Round your intermediate calculations and final answers to 2 decimal places. Leave no cells blank - be certain to enter "0" wherever required.)
Mean Chart Range Chart
UCL
LCL

Answer 1

Kindly check explanation

Explanation:

Sample 1 :

Mean = (79.2 + 78.8 + 80 + 78.4 + 81) / 5 = 79.48

Range = 81 - 78.4 = 2.6

Sample 2 :

Mean = (80.5 + 78.7 + 81 + 80.4 + 80.1) / 5 = 80.14

Range = 81 - 78.7 = 2.3

Sample 3 :

Mean = (79.6 + 79.6 + 80.4 + 80.3 + 80.8) / 5 = 80.14

Range = 80.8 - 79.6 = 1.2

Sample 4 :

Mean =(78.9 + 79.4 + 79.7 + 79.4 + 80.6)/5 = 79.6

Range = 80.6 - 78.9 = 1.7

Sample 5 :

Mean = (80.5 + 79.6 + 80.4 + 80.8 + 78.8)/5 = 80.02

Range = 80.8 - 78.8 = 2

Sample 6 :

Mean =(79.7 + 80.6 + 80.5 + 80 + 81.1)/5 = 80.38

Range = 81.1 - 79.7 = 1.4

Xbar = mean of the means

Xbar = (79.48+80.14+80.14+79.6+80.02+80.38) / 6 = 79.96

Rbar = Mean of the sample ranges

Rbar = (2.6 + 2.3 + 1.2 + 1.7 + 2 + 1.4) / 6 = 1.87

n =5 ;D4 = 2.11 ; D3 = 0

From table, D4 = 2.11 ; D3 = 0

Range chart :

Upper Control limit, UCL = D4 * Rbar ; 2.11*1.87 = 3.9457 = 3.95

Lower Control limit, LCL = D3 * Rbar ; 0*1.87 = 0

Mean chart :

Xbar ± A2 * Rbar

From the table :

n = 5 ; A2 = 0.58

Lower control limit(LCL) = Xbar - A2*Rbar

LCL = 79.96 - (0.58*1.87) = 78.8754 = 78.88

Upper Control Limit (UCL) = Xbar + A2*Rbar

UCL = 79.96 + (0.58*1.87) = 81.0446 = 81.04

(78.88 ; 81.04)

The value of Each sample mean falls within the mean interval, Hence, We can conclude that process is on control.