# standard deviations

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The breaking strength (in pounds) of a certain new synthetic is normally distributed, with a mean of 175 and a variance of 9. The material is considered defective if the breaking strength is less than 166 pounds. What is the probability that a single, randomly selected piece of material will be defective?

• standard deviations -

Z = (score-mean)/SD

Variance = SD^2

Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion related to the Z score.

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