Question 173091
The inside diameter of metal washers produced by a company are normally distributed with a mean of 0.5 inches and a standard deviation of 0.01 inches. Of all washers produced, 0.8% of the washers are rejected because they are to small for a bolt used to test them. What is the diameter of the bolt used for the test? 
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Draw a normal curve and put 0.5" in the middle.
Mark a left tail that has 0.8% of the population in it.
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0.8% = 0.8/100 = 0.008
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Find the z-value below which 0.8% of the population lies.
That z-value is -2.408916...
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Now find the x-value (raw score) that corresponds to that z-value using:
z = (x-u)/sigma
-2.408916 = (x-0.5)/0.01
x-0.5 = 0.01*-2.408916 = -0.024089
x = 0.475910...
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The washer must have had a diameter < 0.475910 inches
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Cheers,
Stan H.