Question

A certain type of pins have average Rockwell hardness 48 units and standard deviation 1.2 units....

A certain type of pins have average Rockwell hardness 48 units and standard deviation 1.2 units. What is the probability that the sample mean of 40 randomly selected pins will be at most 48.12 units?

Math   Statistics-And-Probability   
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Answer #1

Solution :

= / n = 1.2 / 40 = 0.1897

P( 48.12) = P(( - ) / (48.12 - 48) / 0.1897)

= P(z 0.63)

= 0.7357

Probabiliy = 0.7357

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