A reading test is normal with mean 70 and standard deviation 8. Which z-score belongs to a mark of 86?

1. The mark sits above the mean, so the z-score will be positive. 2. Subtract the mean from the mark: 86 minus 70 is 16. 3. Divide that gap by the standard deviation of 8. 4. That gives a z-score of 2. 5. Answering 16 stops at the raw gap and never converts it into standard deviations. _Source: OpenStax High School Statistics (CC BY 4.0), Ch 6 "The Normal Distribution", section 6.1 The Standard Normal Distribution_