in process industry during a daily production run, a total of five (05) samples are collected with four (04) observations within each sample. the sample means (X-Bar) are; 14.5,13.94,16.86,18.77 and 16.64 respectively. the corresponding ranges are; 9.90,7.73,4.51,7.56 and 3.49 repectively . the lower and upper control limits of the x-bar chart are................repectively.

a)12.21,19.91

b)none is correct

c)18.55,13.47

d)11.47,16.55

e)11.21,20.91