9.8 and 9.9

A number that is most representative of an entire collection of numbers is a measure of central tendency. The most commonly used measures of central tendency are mean, median, and mode.

The mean or average can be found by adding all n numbers together and dividing the sum by n. 

The median is the middle number when the numbers are put in order.

The mode is the number that occurs the most frequently. A group of numbers with two modes is called bimodal. 

9.9
Standard Deviation
In statistics and probability theory, the standard deviation shows how much variation or dispersion from the average exists

Box and Whisker Plots
Quartiles can be represented by a box and whisker plot. The five numbers are listed proportionally as if on a number line. They are listed as follows: the smallest number, the lower quartile (The average of the lower half of the data), the median, the upper quartile (the average of the upper half of the data), and the largest number.