Question 12.31

12.31 Accounts receivable.

In an attempt to understand the bill-paying behavior of its distributors, a manufacturer samples bills and records the number of days between the issuing of the bill and the receipt of payment. The manufacturer formed subgroups of 10 randomly chosen bills per week over the course of 30 weeks. It found an overall mean of 30.6833 days and an average standard deviation of 7.50638 days.

Table 12.9: TABLE 12.7 Aluminum percentage measurements
Subgroup Measurements
1 3.99 3.90 3.98
2 4.02 3.95 3.95
3 3.99 3.90 3.90
4 3.99 3.94 3.88
5 3.96 3.93 3.91
6 3.94 3.97 3.83
7 3.89 3.95 3.99
8 3.86 3.97 4.02
9 3.98 3.98 3.95
10 3.93 3.88 4.06
11 3.97 3.91 3.92
12 3.86 3.95 3.88
13 3.92 3.97 3.95
14 4.01 3.91 3.91
15 4.00 4.02 3.93
16 4.01 3.97 3.98
17 3.92 3.92 3.95
18 3.96 3.96 3.90
19 4.04 3.93 3.95
20 3.96 3.85 4.03
21 4.06 4.04 3.93
22 3.94 4.02 3.98
23 3.95 4.07 3.99
24 3.90 3.92 3.97
25 3.97 3.96 3.94
26 3.96 4.00 3.91
27 3.90 3.85 3.91
28 3.97 3.87 3.94
29 3.97 3.88 3.83
30 3.82 3.99 3.84
31 3.95 3.87 3.94
32 3.86 3.91 3.98
33 3.94 3.93 3.90
34 3.89 3.90 3.81
35 3.91 3.99 3.83
  1. Assume that the process is stable in both variation and level. Compute the control limits for the and charts.

    629

  2. Here are the means and standard deviations of future subgroups:
    Week 31 32 33 34 35
    31.1 29.5 33.0 33.4 33.2
    6.1001 10.5013 8.5114 7.5011 3.7059
    Week 36 37 38 39 40
    35.8 37.3 41.5 35.9 36.7
    4.1846 6.5328 8.1548 5.8585 6.7338

    Is the accounts receivable process still in control? If not, specify the nature of the process departure.

12.31

(a) For . Using and . (b) The process variation is in control. The process level is out of control starting at week 38.