Answer:
The variance is  [tex]\sigma ^2 =25[/tex]
Step-by-step explanation:
From the question we are told that
  The sample size is  n =  21
   The sum of squares is [tex]SS = 500[/tex]
Generally the variance is mathematically represented as
      [tex]\sigma ^2 = \frac{SS}{n- 1}[/tex]
substituting values
     [tex]\sigma ^2 = \frac{ 500}{21- 1}[/tex]
     [tex]\sigma ^2 =25[/tex]
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