In a gasoline-blending plant, the quality of the output as indicated by its octane rating is measured for a sample taken from each batch. The observations from 20 such samples are shown below. Construct an I-MR chart for the given data. What can you say about the presence of special causes in the process?

Sample Octane Rating

1 89.2

2 86.5

3 88.4

4 91.8

5 90.3

6 87.5

7 92.6

8 87

9 89.8

10 92.2

11 85.4

12 91.6

13 87.7

14 85

15 91.5

16 90.3

17 85.6

18 90.9

19 82.1

20 85.8