The scores on a standardized test have an average of 1200 wi

The scores on a standardized test have an average of 1200 with a standard deviation of 60. A sample of 36 scores is selected.

What is the probability that the sample mean will be less than 1220? Round your answer to three decimal places.

Solution

P(Xmean < 1220) = 1- P(Xmean ? 1220)

= 1- (P((Xmean - 1200) / (60/sqrt(36)) ? (1220 - 1200)/(60/6)) )

= 1- P(Z ? 2) = 1- 0.0228

= 0.9772 Answer