Question

5-11. A polymer is manufactured in a batch chemical process. Viscosity measurements are normally made on each batch, and long experience with the process has indicated that the variability in the process is fairly stable with 20. Fifteen batch viscosity measurements are given as follows: 724, 718, 776, 760, 745, 759, 795, 756, 742, 740, 761, 749, 739, 747, 742. A process change is made that involves switching the type of catalyst used in the process. Following the process change, eight batch viscosity measurements are taken: 735, 775, 729, 755, 783, 760, 738, 780. Assume that process variability is unaffected by the catalyst change. Find a 90% CI on the difference in mean batch viscosity resulting from the process change. What is the practical meaning of this interval

Answer 1

Explanation:

Confidence interval = 90% = 0.90.

1 - 0.90 = 0.10

Mean of 15 batch:

724+718+776+760+745+759+795+756+742+740+761+749+739+747+742 = 11253/15

= 750.2

Mean of second batch:

735+775+729+755+783+760+738+780

= 6055/8

= 756.875

Sd = 20

Z-alpha/2 = 1.64

= (750.2-756.875)-1.64*√20²/15 + 20²/8

= -21.0348

(750.2-756.875)+1.64*√20²/15 + 20²/8

= 7.68

2. The upper limit of the interval is less than 10 so in conclusion the difference in mean batch viscosity is about 10 or less than 10