Eric has computed that it takes an average (mean) of 17 minutes with a standard deviation of 3 minutes to drive from home, park the car, and walk to his job.

One day it took Eric 21 minutes to get to work. You would use the formula for transforming a raw score in a sample into a z-score to determine how many standard deviations the raw score represents.
Since his "score" is 21, you would subtract the mean of 17 from 21 and divide that result (4) by the standard deviation of 3.
The z-score of 1.33 tells you that Eric’s time to get to work is 1.33 standard deviations from the mean. Another day, it took Eric only 12 minutes to get to work. Using the same formula, determine the z value. Is it positive or negative? Explain why it should be positive or negative

What happens when you subtract 21 from 13?

I do not understand your answer to my question

To determine the z-score for Eric's time of 12 minutes, we can use the same formula as before. Subtracting the mean of 17 from 12 gives us -5. Dividing this result (-5) by the standard deviation of 3 gives us -1.67.

The z-score for Eric's time of 12 minutes is -1.67, which means it is negative.

The reason why it should be negative is that the z-score represents the number of standard deviations a specific data point is above or below the mean. In this case, since Eric's time of 12 minutes is below the mean, it is considered below average. Therefore, the z-score is negative to indicate that it is below the mean.