Only the upper 30% of a normally distributed class passed a quiz for which the mean was 70 and the standard deviation was 10.In this class,76.7 and 78.4 are the boundary limits for students who scored between what percentiles?
A)75th and 80th
B)80th and 85th
C)77th and 80th
D)67th and 80th

Question

Quizplus · Accepted Answer

The z-score for the 30th percentile is -0.524. The z-score for the 70th percentile is 0.524. The z-score for 76.7 is (76.7 - 70) / 10 = 0.67. The z-score for 78.4 is (78.4 - 70) / 10 = 0.84. The percentiles corresponding to these z-scores are 75th and 80th.

Only the Upper 30% of a Normally Distributed Class Passed