A humanities professor assigns letter grades on a test according to the following scheme. A: Top 7% of scores B: Scores below the top 7% and above the bottom 56% C: Scores below the top 44% and above the bottom 19% D: Scores below the top 81% and above the bottom 6% F: Bottom 6% of scores Scores on the test are normally distributed with a mean of 72.1 and a standard deviation of 9.5. Find the minimum score required for an A grade. Round your answer to the nearest whole number, if necessary.

The minimum score required for an A grade is 86.

Step-by-step explanation:

Problems of normally distributed samples can be solved using 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 problem, we have that:

Find the minimum score required for an A grade.

Top 7%, which is the value of X when Z has a pvalue of 1-0.07 = 0.93. So it is X when Z = 1.475. So

The minimum score required for an A grade is 86.

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