statistics

The inside diameter of metal washers produced by a company are normally distributed with a mean of .5 inches and a standdrd deviation of .01 inches. Of all washers produced .8% of the washers are rejected because they are too small for a bolt used to test them. What is the diameter of the bolt used for the test?

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asked by josh
  1. Given:
    μ=0.5"
    σ=0.01"
    Rejection rate = 0.8% = 0.008
    rejection criterion = z<Z
    X=μ+Zσ
    =0.5+0.01Z

    From normal distribution tables
    P(Z<-2.409)=0.008
    so
    X=0.5-0.01*2.409
    =0.4758

    Ans: washers with diameters less than 0.476 are rejected.

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