Question

The time to complete a standardized exam is approximately normal with a mean of 70 minutes & a standard deviation of 10 minutes. Using the 68-95-99.7 rule, if students are given 90 minutes to complete the exam, what percentage of students will not finish?
A. 32%
B. 5%
C. 2.5%
D. 0.0015%

can you show me how you solved the problem?

Answer 1

if the mean is 70 minutes, then 90 minutes is 2 standard deviations above 70. if you look at the bell curve i drew, the percent of exams that took over 90 minutes is 2.5%

let me know if you want me to explain the drawing more, it may be confusing