Twenty samples of subgroup size of 4 (n = 4) were collected for a variable measurement.

Twenty samples of subgroup size of 4 (n = 4) were collected for a variable measurement. Determine the upper control limit (UCL) for an R-chart if the mean of the sample ranges equals 4.4.

Factors for calculating control limits

n             A2           D3           D4

2              1.880     0              3.267

3              1.023     0              2.574

4              0.729     0              2.282

5              0.577     0              2.114

6              0.483     0              2.004 (Points : 10)