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Rockwell hardness of pins of a certain type is known to have a mean value of...

Rockwell hardness of pins of a certain type is known to have a mean value of 50 and a standard deviation of 1.4. (Round your answers to four decimal places.)

(a) If the distribution is normal, what is the probability that the sample mean hardness for a random sample of 13pins is at least 51?


(b) What is the (approximate) probability that the sample mean hardness for a random sample of 42 pins is at least 51?


You may need to use the appropriate table in the Appendix of Tables to answer this question.

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