Question

find the sum of the series 9+11+13+....+91​

Answer 1

Answer:

tn = 91 = a + (n-1)d = l

91 = 9 + (n-1)(2)

82/2 = n-1

n = 41 + 1

n = 42

Sn = n/2 ( a + l)

Sn = 42/2 ( 9+91 )

Sn = 21 ( 100)

Sn = 2100