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Question 70:



No answer provided yet.We need to use z-scores here to figure out the percentile grade cut-offs. We know the mean and standard deviation so we just need to figure out what data point we would use to get the z-scores that correspond to A:90, B:80, C:70, D:60, F:50 percent.
  • The easiest way I can think of doing this is setting up a simple equation and solve for the unknown scores from the z-scores for each percentile.
  • Find the z-scores for the percentiles 90, 80, 70 , 60 (we know 50 is 0). To do this you can use the percentile to z-score calculator.. We’re interested only on one-side of the area of the curve since a negative score is neither possible nor desirable (choose 1-sided) and get the z-scores for all cut-offs. For example you should get 1.28 for 90% (enter .90).
  • Setup the equation for each z-score. For example, for 90% the equation should be ( X – 75 ) / 9 = 1.28. Then isolate and solve for X (X-75 = 11.53396 so X = 86.53). Repeat this process for all scores.
  • You should get the following:


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