Answer:
The numerical limits for a B grade are 72 and 79, that is, a score between 72 and 79 results in a B grade.
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 68.4 and a standard deviation of 9.7.
This means that
Find the numerical limits for a B grade.
Below the 100 - 14 = 86th percentile and above the 65th percentile.
65th percentile:
X when Z has a p-value of 0.65, so X when Z = 0.385.
86th percentile:
X when Z has a p-value of 0.86, so X when Z = 1.08.
The numerical limits for a B grade are 72 and 79, that is, a score between 72 and 79 results in a B grade.