1.

(51 + 52 + 53 + ... + 100) = ?

Answer» Sn = (1 + 2 + 3 + ... + 50 + 51 + 52 + ... + 100) - (1 + 2 + 3 + ... + 50)     = 100 x (1 + 100) - 50 x (1 + 50) 2 2     = (50 x 101) - (25 x 51)     = (5050 - 1275)     = 3775.


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