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# Upper and Lower Limits

A critical dimension of the service quality of a call center is the wait time of a caller to get to a sales representative. Periodically, random samples of 6 (n = 6) customer calls are measured for time. Results from the last eight samples are shown in the following table.

Observation (seconds)
S 1 2 3 4 5 6
1 425 408 422 380 410 401
2 440 450 431 447 422 430
3 402 428 419 434 433 425
4 375 406 395 400 380 390
5 408 407 407 435 411 405
6 398 417 450 418 402 425
7 413 445 390 402 407 410
8 395 402 397 408 400 415

a) Management is willing to use three-sigma limits. Using the factors in the table, determine upper and lower limits for mean and range charts.
b) Plot sample means and ranges on their respective control charts. Is the process in control? Clearly explain what each chart shows.

#### Solution Summary

Control Chart Template is attached that uses three sigma control limits. The analysis of quality control using Control Charts.

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