Question

An X-bar R chart was prepared for an operation using twenty samples with 5 pieces in each sample. X-bar-bar was found to be 33.6and R=bar was 6.2. During production a sample of 5 was taken and the pieces measured 36, 43, 37, 25, and 38. At the time this sample was taken: Select the correct answer:

a. Both the average and range were within control limits.
b. Neither the average nor range were within control limits.
c. Only the average was outside control limits.
d. Only the range was outside control limits.

Answer 1

Answer:

D) Only the range was outside control limits.

Explanation:

The range is the difference between the largest and smallest set of data, or in this case the longest and shortest pieces. In this case, the longest piece measured 43 and the shortest 25, so the range was 18 which is much higher than the control range, 6.2, so it clearly is outside any type of control limit.

The mean of the 5 samples was 35.8, which is only 2.2 away from the mean of the control chart. Even though it is higher than the control mean, the difference represents only 6.5% which can be considered normal.