Q. 2 A5.0( 1 Vote )

Find the sums indicated below:3 + 6 + 9 + ... + 300

Formula used.

Sn = [2a + (n–1)d]

d = an + 1–an

In the sum above A.P follows

Is 3, 6, 9, ……, 300

In the following A.P

a = 3,

d = 6–3 = 3

As the last term is 300

an = a + (n–1)d

300 = 3 + (n–1)3

300 = 3 + 3n–3

3n = 300

n = = 100

Sn = [2a + (n–1)d]

= [2×3 + (100–1)3]

= 50[6 + 99×3]

= 50[6 + 297]

= 15150

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