The following table gives the average and range in kilograms for tensile tests on an improved plastic cord. The subgroup size is 4. Determine the trial central line and control limits. If any points are out of control, assume assignable causes and calculate revised limits and central line.

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Subgroup Number 476 32 466 24 484 32 466 26 470 24 494 24 486 28 496 23 488 24 482 26 49825 464 24 484 24 Subgroup Number 14 15 16 17 18 19 20 21 482 22 506 23 496 23 478 25 484 24 506 23 476 25 485 29 490 25 463 22 469 27 474 22 4 10 23 12 25 13