Question

. The mean number of words per minute (WPM) read by sixth graders is 87 with a population standard deviation of 10. If 60 sixth graders are randomly selected, what is the probability that the sample mean would differ from the population mean by more than 5 WPM?

Answer 1

Solution :

Given that,

mean = = 87

standard deviation = = 10

= / n = 10 / 60 = 1.2910

= 1 - P[(-5) / 1.2910< ( - ) / < (5) / 1.2910)]

= 1 - P(-3.87 < Z < 3.87)

= 1 - P(Z <3.87 ) - P(Z < -3.87)

= 1 - P(0.9999 - 0.0001)

= 1 - 0.9998

= 0.0002

Probability = 0.0002