find

Asked by  | 3rd Oct, 2008, 07:47: PM

Expert Answer:

Σn=210 

n(n+1) /2 = 210

n(n+1) = 420

21 x 20 = 420  so n= 20

Σn2 = n(n+1) (2n+1) / 6 = 420 x 41 / 6 = 2870

 

Answered by  | 11th Oct, 2008, 09:58: PM

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