Thread: Help

Is there a correct answer found in my choices. I could not find one.

A sample of 25 is taken from a population which has a normal distribution with a mean of 60 and standard deviation of 15. The probability that the sample mean is between 55.5 and 64.5 is?

A. .0668
B. .2668
C. .5468
D. .8664
E. .9332

Originally Posted by NICEKID

Is there a correct answer found in my choices. I could not find one.

A sample of 25 is taken from a population which has a normal distribution with a mean of 60 and standard deviation of 15. The probability that the sample mean is between 55.5 and 64.5 is?

A. .0668
B. .2668
C. .5468
D. .8664
E. .9332

D looks right. The sample mean has standard deviation 15/sqrt(25) = 3, so 54.5 is 1.5 standard deviations below the mean and 64.5 is 1.5 standard deviations above.

Right, you can look up z = 1.5 in a table of standard normal probabilities and find the probability in the tail is 0.668 so two tails is 0.668*2 = 0.1336, subtract from one and you get 0.8664.