A researcher records the following times (in seconds)that it took a group of students to complete an exam: 18 ± 2 (M ± SD)min.How long did it take 80% of students to complete the exam?
A) less than 16 min
B) 16.32 min
C) less than 18 min
D) 19.68 min

Question

Quizplus · Accepted Answer

The times are normally distributed with a mean (M) of 18 minutes and a standard deviation (SD) of 2 minutes. To find the time it took 80% of students, we look for the 80th percentile in a normal distribution, which corresponds to a z-score of approximately 0.84. Using the formula: time = M + (z * SD), we get 18 + (0.84 * 2) = 19.68 minutes.

A Researcher Records the Following Times (In Seconds)that It Took