Answer:
Option C) 2.5%
Step-by-step explanation:
We are given the following information in the question:
The distribution of time to complete a standardized exam is approximately normal.
- The empirical rule states that for a normal distribution,the data will fall within three standard deviations of the mean.
- 68% of data falls within the first standard deviation from the mean that is

- 95% fall within two standard deviations that is

- 99.7% fall within three standard deviations that is

The students are given 90 minutes to complete the exam.

Around 95% of the students will fall in this interval
.
Around 5% will not fall into this interval.
Thus, around 2.5% of the students will not be able to complete their test in 90 minutes.
We considered 2.5% only because the remaining 5% of students would lie on both sides of the mean. Our requirement was only to calculate students who would not be able to complete test even in 9- minutes so we divided this percentage by 2.