We have asked to find the sum of all the multiples of 9 lying between 300 and 700.
Sir please give me a detailed solution of this question as it is very important for examination
ML Aggarwal Avichal Publication Arithmetic Progression chapter 9 question no 20 iii
Multiples of 9 lying between 300 and 700=306,315,324,333,......,693
Here, a=306,d=9 and l=693
We know that, l=a+(n−1)d
693=306+(n−1)×9
(n−1)×9=693−306=387
n−1=9387=43
n=43+1=44
There are 44 terms.
Find the sum of 44 terms:
S44=2n[a+l]
=244[306+693]
=22×999=21978.