The Mathematics section of the ACT test had a mean of 20.9 and an SD of 5.3 for the years 2013–2015. Suppose these are well modeled by a Normal distribution. ​a) About what percent of students scored over 33? ​b) About what percent of students scored under 16? ​c) About what percent of students scored between 16 and 33?

Features Features Normal distribution is characterized by two parameters, mean (µ) and standard deviation (σ). When graphed, the mean represents the center of the bell curve and the graph is perfectly symmetric about the center. The mean, median, and mode are all equal for a normal distribution. The standard deviation measures the data's spread from the center. The higher the standard deviation, the more the data is spread out and the flatter the bell curve looks. Variance is another commonly used measure of the spread of the distribution and is equal to the square of the standard deviation.