Hi Normal distribution: Using TI or similarly an inexpensive Casio fx-115 ES plus: area under the standard normal distribution curve(continuous) is the same as the Probability of the given z-score: P( |z| ≤ -2.31) is 2P(z ≤ -2.31) = 2(.0104) = .0208 Wish You the Best in your Studies. Shown below is the positioning of |z| = 2.31 on the Standard Normal Curve