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Posted by on Sunday, April 7, 2013 at 10:17am.

A large metropolitan area found that the time it takes for people to commute to work has a mean of 20.5 minutes and a standard deviation of 15.4 minutes. What is the probability that a random sample of 40 people have a mean commute time greater than 25 minutes?

  • AP Stats (math) - , Sunday, April 7, 2013 at 11:04am

    z-score = (25-20.5)/15.4

    then look up that z in your tables,
    subtract that from 1
    that is,
    1 - value you looked up

    or

    you can use one of my favourite websites

    http://davidmlane.com/normal.html

    Make sure "area from value " is clicked on
    enter the mean, the sd, and click on "below" and enter 25
    The value of .6149 should agree with the value you found above

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