# Help

• Apr 29th 2005, 02:30 PM
NICEKID
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
• Apr 29th 2005, 07:58 PM
hpe
Quote:

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.
• May 13th 2005, 02:18 PM
billh
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.