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Answer:
The numerical limits for a D grade is between 57 and 64.
Step-by-step explanation:
When the distribution is normal, we use the z-score formula.
In a set with mean and standard deviation
, the zscore of a measure X is given by:
The Z-score measures how many standard deviations the measure is from the mean. After finding the Z-score, we look at the z-score table and find the p-value associated with this z-score. This p-value is the probability that the value of the measure is smaller than X, that is, the percentile of X. Subtracting 1 by the pvalue, we get the probability that the value of the measure is greater than X.
In this question:
D: Scores below the top 80% and above the bottom 7%
Between the 7th and the 100 - 80 = 20th percentile.
7th percentile:
X when Z has a pvalue of 0.07. So X when Z = -1.475.
So 57
20th percentile:
X when Z has a pvalue of 0.2. So X when Z = -0.84.
So 64
The numerical limits for a D grade is between 57 and 64.