Question

R3. 56:

The Billing department of a firm has been keeping an np chart on defective invoices. They sample 50 invoices a week and over the past year their average number of defective invoices per week has been 4.1. In order to save time, they are going to reduce the sample size to 40. What are the new control limits for the np chart with sample size of 40?

1. A. 2.182 and 6.018 B. 0 and 9.920 C. 0 and 7.936 D. 0 and 9.854

Answer 1

solution:

average number of defective invoices over the past week = np = 4.1

where n is the total number of invoice inspected

and p is the proportion of defective invoices

np= 4.1 and n = 40

so p = 4.1 / 40 = 0.1025

new control limit for np chart =

so upper control limit = 4.1 + 5.754 = 9.854

lower limit = 4.1 - 5.754 = -1.6 as it not goes lower than zero so it is 0

ans is 0 and 9.854