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

4 years ago


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

4 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
To Win!!!
Click Here for details
chapter wise weightage
Hello Student, Pls specify which chapters ????? Thanks,...
Nishant Vora 2 months ago
are computer based exams in aieee more difficult than paper and pen
That totally depends on how much familiar one is with the use of computers. If one uses computers on a regular basis, it actually becomes easier to attempt the paper online as it would save...
Ravi one month ago
thanks sir
Mohammad Dilshad one month ago
I am taking my board exams through NIOS [2015] and while applying for the JEE main, there is a column to specify the name and address of the school. Since I am not enrolled in any...
Hello Student, In case of any confusion you can post it tojeemain[at]nic[dot]in or call them. Go to thejee 2015 website Because ultimately they are the deciders not we. Thanks,...
Nishant Vora one month ago
Thanks for the reply sir. I am also worried whether there might be any clash in the exam dates. As both of them are due April.
Elamparithi one month ago
sir i want to know that which iit is best for b.tech in computer science ???????????
All IITs are best as per the branch. It depends on the rank which u get to get into an IIT. I can give you a rough estimate about the ranking ...as the trends change every year but roughly...
Ramesh V 5 years ago
It cant be said that which iit is best for computer science but one thing can be said that iit delhi has one of the most challenging curriculum and very good fascilities for engineering in...
AskiitianExpert Vinayak-iitd 5 years ago
what is the meaning of java is platform independent language? what is it significance?
Java solves the problem of platform-independence by using byte code. The Java compiler does not produce native executable code for a particular machine like a C compiler would. Instead it...
Shane Macguire 5 years ago
Where CSE is better? NIT Warangal or COEP and if I get Mech at NITW also CSE with COEP then what should i choose?My likelihood ie CSE or good college ie NITW for Mech?
Undoubtedly NITW ia very good college for both mech and CSE. It is far better than COEP for CSE. But whether to take CSE in COEP or MECH in NITW depends on your interested branch and also...
Ramreddy 5 months ago
Thank you so much but I wanna know if fee structure at NITW for MECH is less for SC candidates?
VINAY GEDAM 5 months ago
View all Questions »