Find the sum of series 103=101+99+..............49.

a= 103, d=-2, an=49 Sn = ?

an = 49

a + (n-1)d = 49

103 + (n-1)(-2) = 49

(n-1)(-2) = -54

(n-1) = 27

n = 28

Sn = n/2 [a + an]

S28 = 14 (103 + 49)

S28 = 14* 152 = 2128

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