7.64 Lumber Specs The manager of a building-supplies company randomly samples incoming lumber to see whether it meets quality specifications. From each shipment, 100 pieces of 2 x 4 lumber are inspected and judged according to whether they are first (acceptable) or second (defec- tive) grade. The proportions of second-grade 2 4s recorded for 30 shipments were as follows:

Construct a control chart for the proportion of second- grade 2 4s in samples of 100 pieces of lumber. Explain how the control chart can be of use to the manager of the building-supplies company.

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0.14 0.21 0.19 0.18 0.23 0.20 0.25 0.19 0.22 0.17 0.21 0.15 0.23 0.12 0.19 0.22 0.15 0.26 0.22 0.21 0.14 0.20 0.18 0.22 0.21 0.13 0.20 0.23 0.19 0.26