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    kakaroto's Avatar
    kakaroto Posts: 2, Reputation: 1
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    #1

    Jul 23, 2009, 01:09 PM
    statistics-normal distribution
    well I need help... I have tried many times but can't figure this one out.

    The waist measurement of students in a college is normally distributed. The standard deviation is known to be 5 inches. It is found that 15% of the students have waist sizes less than 28 inches. What proportion of students will have waits between 30 and 35 inches ?
    A. 0.3795 b. 0.2389 c.0.1406 d.0.0983 e. none of the above

    OK if 15% have less than 28 inches so the proportion lies on the 85% left which should be x>28. I'm stuck from here... help
    galactus's Avatar
    galactus Posts: 2,271, Reputation: 282
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    #2

    Jul 23, 2009, 01:48 PM
    Look up the z-score for .15. We see it is -1.04

    Use

    Now, solve: for

    That is the mean.

    Then, you have what you need to find the percentage between 30 and 35 by using the same formula, finding the percentages and subtracting them.
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