How to solve this statistics question?

Posted on 2016-05-11 17:55:00 in Statistics by LEXODUS

28 students take a statistics test and receive the following grades. 
57 75 90 70 60 61 85 
65 81 83 72 63 81 70 
100 82 79 78 82 78 87 
98 58 91 84 90 83 81 
Using Chebyshev's theorem and the emperical rule, how many values would you expect to fall 
within two standard deviations of the mean? How many values actually fall within two standard 
deviations the mean? 

Mean is 78, Σx^2 is 173990, can't really figure the rest

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