Question

Find the sum of first 20 term of the series 4+7+10_ _ _ _

Answer 1

Here a =4

d=3

n=20

Sn=n/2{ 2a+(n-1)d}

=20/2{2*4+(20-1)3}

=10(8+19*3)

=10(8+57)

=10*65

=650