SOLUTION: There are 330 students at Valley Central High School enrolled in Chemistry. On the April report card, the students' grades are approximately normally distributed with a mean of 78

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Question 1159285: There are 330 students at Valley Central High School enrolled in Chemistry. On the April report card, the students' grades are approximately normally distributed with a mean of 78 and a standard deviation of 7.9. Students who earn a grade less than or equal to 64.9 must attend summer school. The number of students who must attend summer school for Chemistry is closest to
Answer by VFBundy(438) About Me  (Show Source):
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z-score = %2864.9+-+78%29%2F7.9 = -13.1%2F7.9 = -1.66

Look up -1.66 on a z-table. The result is 0.0485. This means 4.85% of the 330 students will have to attend summer school:

330 * 0.0485 = 16