Q3 of 85 Page 104

For a given A.P. with

a = 1, d = 2, find S10.

Formula used.


Sn = [2a + (n–1)d]


d = an + 1–an


In the following A.P


⇒ a = 1,


⇒ d = 2


⇒ n = 10


Sn = [2a + (n–1)d]


= [2×1 + (10–1)2]


= 5[2 + 9×2]


= 5[2 + 18]


= 100


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