Normal Distribution and Standard Deviation

                     Lesson 1


                                                            Problem:   Find the percentage of the normally distributed data that lies within 2 standard deviations of the mean.


                                                            Solution    Percentages from -2 to +2 standard deviations.       

                                                            Step 1:                      


                                                            Solution    4.4%+9.2%+15.0%+19.1%+19.1%+15.0%+9.2%+4.4% = 95.4%

                                                            Step 2:                                                                                          


                                                            Solution     Answer: 95.4%                                                         

                                                            Step 3:                                                                                       



                                                             Try two practice problems:  


                                                                                 Solve the following:




Johnny’s scores in a subject this semester were rather inconsistent:  165, 230, 120, 100, 90, 125, 75.For this population, how many scores are within one standard deviation of the mean?


A group of 423 people has a mean age of 16.4 years with a standard deviation of 0.6 years.  The ages are normally distributed.  How many people are younger than 15.2 years?  Express answer to the nearest people?









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