Please note that there is an error in last page of the tutorial notes, the correct formula for the Standard Deviation of Combined Random Variables (the student notes contain the correction as shown below)
Source: Created by Emily LeBlanc-Perrone using Brase, C., & Brase, C. (2012). Understandable statistics: Concepts and methods. (10th ed.). Boston, MA: Brooks/Cole Cengage Learning. and Hinders, D. (2011). 5 steps to a 5: Ap statistics. McGraw-Hill.