Question

The mean length of time, per week, that students at a certain school spend on their homework is 24.3 hours, with a standard deviation of 1.4 hours. Assuming the distribution of study times is normal, what percent of students study between 22.9 and 25.7 hours

Answer 1

Approximately 68% of students study between 22.9 and 25.7 hours.

Explanation:

The Empirical Rule states that, for a normally distributed random variable:

Approximately 68% of the measures are within 1 standard deviation of the mean.

Approximately 95% of the measures are within 2 standard deviations of the mean.

Approximately 99.7% of the measures are within 3 standard deviations of the mean.

In this problem, we have that:

Mean of 24.3 hours, standard deviation of 1.4 hours.

What percent of students study between 22.9 and 25.7 hours?

22.9 = 24.3 - 1.4

25.7 = 24.3 + 1.4

Within 1 standard deviation of the mean, so:

Approximately 68% of students study between 22.9 and 25.7 hours.