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

3 years ago

Share

Answers : (1)

                    

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.




Please feel free to post as many doubts on our discussion forum as you can. We are all IITians and here to help you in your IIT JEE preparation.


Now you can win exciting gifts by answering the questions on Discussion Forum. So help discuss any query on askiitians forum and become an Elite Expert League askiitian.



Win exciting gifts by answering the questions on Discussion Forum




3 years ago

Post Your Answer

More Questions On IIT JEE Entrance Exam

Ask Experts

Have any Question? Ask Experts
Post Question
 
Answer ‘n’ Earn
Attractive Gift
Vouchers
To Win!!!
Click Here for details
what is the selection procedure for iit jee 2015 exam????
 
 
There has been speculation going around that JEE Mains and JEE Advanced will merged from 2015. If that is the case,then one has to clear one exam.If the present system is followed then...
  img
Aziz Alam 15 days ago
how to score above 100 in mathematics in jee advanced
 
 
There is no definite way to to get a particular number of marks.But there are methods through which you can gradually achieve a level of comfort which would be sufficient for you to get 100...
  img
Aziz Alam 12 days ago
Sir is it better to take eee in nit silchar or cs in nit agartala or sikkim or megalaya.can I get these branches in even spot round if my jee mains air will be around 50000 .general...
 
 
All nits are very good.try for any nit.
 
Rak 20 days ago
 
These are the New NITs located far away from Multinational Cities , Placements may vary In these colleges but you can try to get admission In Institutions under your ranking like nit silchar...
 
Vivek Kumar 20 days ago
Is AIR category rank considered for jee main counselling for general students?
 
 
For JEE Main counselling, AIR overall is considered. But the quota is there according which seats are alotted.Seats would be alotted according to quota but AIR overall rank would be...
  img
Aziz Alam 7 days ago
scoring topics in iit jee
 
 
MATHS: CO-ORDINATE:- straight line, circle, locus. ALGEBRA:- complex no.,qudratic equation,probability,a.p.,g.p. CACULUS:-LIMIT,CONTINUTY,integration,application of calculus. Trigonometry...
  img
Sourabh Singh 10 days ago
View all Questions »