Find the sum of the integers between 100 and 200 that are divisible by 9.

Explanation

Number between `100−200` divisible by `9`
are `108,117,126,...198`

Here,
`a=108.d=117−108=9 ` and `a_n​=198`

`=>a_n=a+(n-1)d`

`=>a+(n−1)d=198`

`=>108+(n−1)9=198`

`=> n=11`

Now, `S_n​=n/2​[2a+(n−1)d]`

`=> S_(11)​=(11)/2​[2(108)+(11−1)(9)]`

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