6. Control charts for X and s are to be established on the Brinell hardness of hardened tool steel in kilograms per square millimeter. Data for subgroup sizes of 8 are shown below. Determine the trial central line and control limits for the X and s charts. Assume that the out-of-control points have assignable causes. Calculate the revised limits and central line.

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Subgroup Number X S Subgroup Number X S 1234567890=22 540 26 14 551 24 534 23 15 522 29 545 24 16 579 26 561 27 17 549 28 576 25 18 508 23 523 50 19 569 22 571 29 20 574 28 547 29 21 563 33 584 23 22 561 23 552 24 23 548 25 11 541 28 24 556 27 545 25 25 553 23 546 26