Question

find the sum of all multiples of 9 between 300-700​

Answer 1

Step-by-step explanation:

first multiple of 9 between 300-700, a=306

last multiple of 9 between 300-700, an=693

common difference, d=9

we know that

an=a+(n-1)d

693=306+(n-1)9

693=306+9n-9

693-306+9=9n

396=n

44=n

now,

Sn=n/2(a+an)

=44/2(306+693)

=22(999)

=1998

therefore sum of all multiples of 9 between 300-700 is 1998.