Question

While developing x-bar and R charts, the manager took 10 samples each of size 6. The average of sample means was 3.2. The average range value was 0.6. What will be the value of UCL for the R-chart?

a. 1.2
b. 1.4
c. 1.5
d. 1.7

Answer 1

Option a. 1.2 is the correct answer

Explanation:

Given the data in the question;

sample size n = 10

sub group = 6

The average of sample means x" = 3.2

Average range value R' = 0.6

the value of UCL for the R-chart = ?

To get the value of UCL for the R-chart, we say;

`UCL_R` = D₄ × R'

from table of constants "Tabular values for x-bar and range charts

for size 6, the factor for control limits for range D₄ = 2.004

so we substitute

`UCL_R` = 2.004 × 0.6

`UCL_R` = 1.2024 ≈ 1.2

Hence, Option a. 1.2 is the correct answer.