Rockwell hardness of pins of a certain type is known to have amean value of 50 a

Question

Rockwell hardness of pins of a certain type is known to have amean value of 50 and a standard deviation of 1.2.

a). If the distribution is normal, what is the probability thatthe sample mean hardness for a random sample of 9 pins is at least51?

b). What is the (approximate) probability that the samplemean hardness for a random sample of 40 pins is at least 51?

Explanation / Answer

Given =50, =1.2 (a) n=9 P(xbar >= 51) = P( [xbar - ]/[/n] >=(51-50)/(1.2/sqrt(9) ) = P(Z>2.5)= 0.0062 (check normaltable) (b) n=40 P(Z>= (51-50)/(1.2/sqrt(40))) =P(Z > = 5.27 ) ˜0 (checknormal table)

Related Questions

Navigate

• Browse (All)
• Browse R
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.