Suppose that a Normal model describes the acidity (pH) of rainwater, and that water tested after last week's storm had a z-score of 1.8. This means that the acidity of that rain…
A) had a pH 1.8 times that of average rainwater.
B) varied with a standard deviation of 1.8
C) had a pH 1.8 higher than average rainfall.
D) had a pH 1.8 standard deviations higher than that of average rainwater.
E) had a pH of 1.8.

Question

Quizplus · Accepted Answer

A z-score of 1.8 means the observation is 1.8 standard deviations above the mean of the Normal distribution. In this case, the observation refers to the pH of rainwater, so the rainwater tested had a pH that was 1.8 standard deviations higher than the average pH of rainwater. Therefore, the answer is D.

Suppose That a Normal Model Describes the Acidity (PH) of Rainwater