Question

Find the sum of all multiples of 9lying between 300 and 700

Answer 1

Multiples of 9 lying between 300 and 700 are 306,315,324,...,693.

Here, a=306

d=9

l=639

We know,

l=a+(n-1)d

=>639=306+(n-1)9

=> 333=(n-1)9

=>n-1=37

=>n=38

Now,sum,S

=n/2(a+l)

=38/2(306+639)

=19*945

=17955