Question

Thompson and Thompson is a steel bolts manufacturing company. Their current steel bolts have a mean diameter of 145 millimeters, and a standard deviation of 7 millimeters.

If a random sample of 31 steel bolts is selected, what is the probability that the sample mean would be greater than 141.5 millimeters? Round your answer to four decimal places.

Answer 1

Solution :

Given that ,

mean = = 145

standard deviation = = 7

n = 31

= 145

= / n = 7 / 31

P( > 141.5) = 1 - P( < 141.5)

= 1 - P[( - ) / < (141.5 - 145) / 7 / 31 ]

= 1 - P(z < -2.78)

= 0.9973