Question

If a teacher is grading on a curve, the median is 78 and the standard deviation is 9.6, how do i find out the ranges for grades? ex, an A is the top 15% of the curve. I know it has to do with the z score and that is the # of standard deviations the score is from the median, but i am totally confused how to use this information to get the grade ranges.
Unless the curve is normal, the median and mean may not be the same and you cannot calculate the percentages with a Z score.

Z = (score-mean)/SD

Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability (.15) and its Z score. Insert data inot above equation.

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