Question

Brittany uses a stopwatch to time how long it takes each day for her school bus to travel from her house to school. She finds that the times are distributed normally, with a mean of 21 minutes and a standard deviation of 2 minutes. If there are 180 school days each year, approximately how many times in Brittany's four years of high school will the school bus take more than 27 minutes to travel from Brittany's house to school? A. 18 B. 36 C. 1 D. 4

Answer 1

C.1

Explanation:

On edmentum this is correct.

Answer 2

C

Explanation:

We start by calculating the z-score of 27 minutes

Mathematically z-score = (x-mean)/SD

FROM the question, mean = 21 and SD = 2

so z-score = (27-21)/2 = 6/2 = 3

The probability we want to calculate is P(z > 3)

we proceed to the standard normal distribution table to get this

P(z > 3) = 0.0013499

Now seeing this, we want to calculate the number of days.

Since there are 180 days in a year and we have 4 years, the total number of days = 180 * 4 = 720 days

The number of days in which the school bus took more than 27 minutes will be ;

720 * 0.0013499 = 0.971928 which is approximately 1