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```        If Sn denotes the sum to n terms of the series 1<=n<=9
1+22+333+......+999+...... , then for n=>2
(9 times)

a). Sn-Sn-1=1\9(10n-n2+n)                           b).S
c). 9(Sn-Sn-1)=n(10n-1)                               d).S3= 356```
7 years ago

68 Points
```										Dear swapnil ,
there is a method of solving objective questions called solving by elimination. although we can try about solving for Sn -Sn-1 but in case of objective exams where speed matters it is better to use the former one.
so here , Sn -Sn-1 = an  , i.e. nth term.
a) apply n=2 , we get a2 not equal to 22 so the option is eliminated.
b) not clearly mentioned by you.
c)apply two a2 is 22 but it you shud check also for n =9 where it gives wrong answer so option is eliminated.
d) manually see it is right .
so option d is correct.

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```
7 years ago
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