Posted by Christina on Monday, March 18, 2013 at 9:03am.
The average age of a vehicle registered in the United States is 8 years, or 96 months. Assume the standard deviation is 16 months. If a random sample of a group of 48 vehicles is selected find the probability that the mean of the groupâ€™s age is between 90 and 100 months.
The answer I got was .9536803695 is the correct?

Stats.  PsyDAG, Monday, March 18, 2013 at 12:13pm
SEm = 16/√48 = 16/6.9282 = 2.3
Z = (scoremean)/SEm = (10096)/2.3 = 1.7
Z = (scoremean)/SEm = (9096)/2.3 = 2.6
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability related to the Z scores.
.4554 + .4953 = .9507
Yep, .95 is close enough

Stats.  Christina, Monday, March 18, 2013 at 12:51pm
Thank you so much
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