1+2+3+4+-----+20= কত?

A 210

B 212

C 214

D 220

Solution

Correct Answer: Option A

আমরা জানি ,
         সমষ্টি s = n(n+1)/2
                     =20(20+1)/2   [এখানে n =20]
                      =10×21
                      =210

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