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Posted by 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 group’s age is between 90 and 100 months.


The answer I got was .9536803695 is the correct?

  • Stats. - , Monday, March 18, 2013 at 12:13pm

    SEm = 16/√48 = 16/6.9282 = 2.3

    Z = (score-mean)/SEm = (100-96)/2.3 = 1.7

    Z = (score-mean)/SEm = (90-96)/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. - , Monday, March 18, 2013 at 12:51pm

    Thank you so much

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