An article in the Journal of Aircraft (1988) describes the computation of drag c

Question

An article in the Journal of Aircraft (1988) describes the computation of drag coefficients for the NASA 0012 airfoil. Different computational algorithms were used at = 0.7 with the following results (drag coefficients are in units of drag counts; that is, one count is equivalent to a drag coefficient of 0.0001): 79, 99, 76, 83, 81, 85, 82, 80, and 84. Compute the sample mean, sample variance, and sample standard deviation. Round your answers to 2 decimal places. The sample mean is drag counts. The sample variance is (drag counts)^2. The sample standard deviation is drag counts.

Explanation / Answer

Getting the mean, X,          
          
X = Sum(x) / n          
Summing the items, Sum(x) =    749      
As n =    9      
Thus,          
X =    83.22222222   [ANSWER, SAMPLE MEAN]

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consider:  

          
          
Thus, Sum(x - X)^2 =    339.5555556      
          
Thus, as           
          
s^2 = Sum(x - X)^2 / (n - 1)          
          
As n =    9      
          
s^2 =    42.44444444   [ANSWER, SAMPLE VARIANCE]  
          
Thus,          
          
s =    6.514940095   [ANSWER, SAMPLE STANDARD DEVIATION]  

x x - X (x - X)^2 79 -4.22222 17.82716 99 15.77778 248.9383 76 -7.22222 52.16049 83 -0.22222 0.049383 81 -2.22222 4.938272 85 1.777778 3.160494 82 -1.22222 1.493827 80 -3.22222 10.38272 84 0.777778 0.604938

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