SOLUTION: Scores on a test are approximately normally distributed with a mean of 70 and a standard deviation of 9. The teacher wants to give A's to the top 10% of students. What is the botto

Question 964221: Scores on a test are approximately normally distributed with a mean of 70 and a standard deviation of 9. The teacher wants to give A's to the top 10% of students. What is the bottom cutoff for an A grade? Round your answer to he nearest whole number.
Answer by rothauserc(4718) (Show Source): You can put this solution on YOUR website!
z-score associated with 90% is 1.28, then
1.28 = (x - mean) / std dev. = (x - 70) / 9
x - 70 = 9 * 1.28
x -70 = 11.52
x = 81.52 approx 82
therefore, 82 is the bottom cutoff for an A grade
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