Mining Engineering > GATE 2023 > Mineral Processing
In a quality control process of coal supplied to a thermal plant, the 3-sigma control limits for fixed carbon (FC) are defined by 40%±15%. The process is termed "out of control" if:
Rule 1: 4 out of 5 successive values of FC are situated at the same side of the mean and at a distance more than 1 standard deviation.
Rule 2: Any one value crosses any of the 3-sigma control limits.
For the following continuous data of FC (%): 49, 51, 56, 20, 46, 48, 47, 49, 45, 41, 42, 40, the process is
A
out of control because of both rules 1 & 2.
B
out of control because of rule 1 only.
C
out of control because of rule 2 only.
D
not out of control.

Correct : c

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