Question

The candy produced by a company has a sugar level that is normally distributed with a mean of 16.8 grams and a standard deviation of 0.7 grams. The company takes readings of every 10th bar off the production line. The reading points are 17.3, 14.9, 18.3, 16.5, 16.1, 17.4, 18.4. Is the process in control or out of control and why?

Answer 1

It is not in control because at least two of the of the data points are more than 2 standard deviations from the mean are far apart.

18.3,18.4 > 18.2 Upper Control limit

14.9, > 15.4 Lower Control Limit

Explanation:

Find the limits using μ ± 3σ and μ ± 2σ

Using μ ± 3σ

Upper Control Limit = μ + 3σ = 16.8 + 3(0.7)= 16.8 + 2.1= 18.9

Lower Control Limit = μ - 3σ =16.8 - 3(0.7)= 16.8 - 2.1= 14.7

Using μ ± 2σ

Upper Control Limit = μ + 2σ = 16.8 + 2(0.7)= 16.8 + 1.4= 18.2

Lower Control Limit = μ - 2σ =16.8 - 2(0.7)= 16.8 - 1.4= 15.4

The data points are 17.3, 14.9, 18.3, 16.5, 16.1, 17.4, 18.4.

Rearranging these data points 14.9, 16.1, 16.5, 17.3, 17.4, 18.3,18.4.

We see from the above that it is out of control because the values jump above and below the mean.

It is not in control as two of the of the data points are more than 2 standard deviations from the mean are far apart.