Hi,

Mrs. Jones Algebra 2 class scored very well on yesterday’s quiz: 91, 92, 94, 88, 96, 99, 91, 93, 94, 97, 95, 97 

With one exception, everyone received an A. Within how many standard deviations from the mean do all the quiz grades fall? 

Mean =  93.9 , SD = 3.12  (Using Excel Data Analysis Tool)

 (99-93.9)/3.12 = 1.6 

 (88 - 93.9)/3.12 = -1.89

all the quiz grades fall within 2 SD from the mean.

Important to Understand z -values as they relate to the Standard Normal curve:

Below:  z = 0, z = ± 1, z= ±2 , z= ±3 are plotted.  

Note: z = 0 (x value the mean) 50% of the area under the curve is to the left and 50% to the right





  

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