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Answer:
The numerical limits for a B grade are 81 and 89, that is, a score between 81 and 89 gets a B grade.
Step-by-step explanation:
Normal Probability Distribution:
Problems of normal distributions can be solved using the z-score formula.
In a set with mean and standard deviation
, the z-score 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 p-value, we get the probability that the value of the measure is greater than X.
Scores on the test are normally distributed with a mean of 79.7 and a standard deviation of 8.4.
This means that
B: Scores below the top 13% and above the bottom 56%
So between the 56th percentile and the 100 - 13 = 87th percentile.
56th percentile:
X when Z has a p-value of 0.56, so X when Z = 0.15. Then
87th percentile:
X when Z has a p-value of 0.87, so X when Z = 1.13.
The numerical limits for a B grade are 81 and 89, that is, a score between 81 and 89 gets a B grade.