Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized for You

we will pick new questions that match your level based on your Timer History

Track Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

It appears that you are browsing the GMAT Club forum unregistered!

Signing up is free, quick, and confidential.
Join other 500,000 members and get the full benefits of GMAT Club

Registration gives you:

Tests

Take 11 tests and quizzes from GMAT Club and leading GMAT prep companies such as Manhattan GMAT,
Knewton, and others. All are free for GMAT Club members.

Applicant Stats

View detailed applicant stats such as GPA, GMAT score, work experience, location, application
status, and more

Books/Downloads

Download thousands of study notes,
question collections, GMAT Club’s
Grammar and Math books.
All are free!

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

The reason why I have splited 4 = 2+2 ; 7 = 4+3 ; 11 = 5+7, is since the difference between the consecutive terms are in AP, if I subtract that difference from the particular term of the sequence I will get the previous term. This way I can split the whole sequence into an AP sequence and the given sequence with n-1 terms.

this way I can get \(S_n\) and \(S_{n-1}\) _________________

Re: Help:Tough problem on exponential sequence [#permalink]
24 Jul 2010, 20:18

1

This post received KUDOS

I've learnt this method at school, and it can be applied easily to a wide variety of problems tht involve summations.

On observation we find that the 'n'th term of this sequence is of the form

\(T_n=T_{n-1}+ [n-1]\)

for n >= 2 i.e from the 2nd term onwards.

so to find the 60th term (\(T_60\)) all we need to do is this :

\(T_{60} = T_{59} + (60-1) = T_{59}+59\) \(T_{59} = T_{58}+58\) and so on . . . . \(T_3 = T_2+2\) \(T_2 = T_1+1\) ___________

On summing all the equations' left hand sides and right hand sides, observe that every equations' LHS (starting with the second) cancels with the term in the RHS above it - for example T59 in the second eqn in the LHS cancels with T59 in the RHS of the first equation and so on for the entire system of equations.

After this huge crash of dominoes, all we are left with is

\(T_{60} = T_1 + (1+2+3+4+...59)\)

\(1+2+...59\) as we know is \({59*(59+1)}/2 = 1770\) and \(T_1 = 1\)

Re: Help:Tough problem on exponential sequence [#permalink]
28 Jan 2011, 11:16

2

This post received KUDOS

Expert's post

144144 wrote:

I might missing something small... how u done 1+2+3+4+5+6+7+8+9+10....+59+60 in a short way? can someone please explain the logic?

is there a difference if the amount of numbers is an even or uneven number?

thanks a lot.

First of all we have 1+(1+2+3+...+59).

Next, the sum of the elements in any evenly spaced set is given by: \(Sum=\frac{first+last}{2}*# \ of \ terms\), the mean multiplied by the number of terms. So, \(1+(1+2+3+...+59)=1+\frac{1+59}{2}*59=1+1770=1771\).

Re: Help:Tough problem on exponential sequence [#permalink]
28 Jan 2011, 11:41

Bunuel wrote:

144144 wrote:

I might missing something small... how u done 1+2+3+4+5+6+7+8+9+10....+59+60 in a short way? can someone please explain the logic?

is there a difference if the amount of numbers is an even or uneven number?

thanks a lot.

First of all we have 1+(1+2+3+...+59).

Next, the sum of the elements in any evenly spaced set is given by: \(Sum=\frac{first+last}{2}*# \ of \ terms\), the mean multiplied by the number of terms. So, \(1+(1+2+3+...+59)=1+\frac{1+59}{2}*59=1+1770=1771\).

Re: What is the sixtieth term in the following sequence? 1, 2, 4 [#permalink]
20 Oct 2014, 12:43

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email. _________________

Low GPA MBA Acceptance Rate Analysis Many applicants worry about applying to business school if they have a low GPA. I analyzed the low GPA MBA acceptance rate at...

http://blog.davidbbaker.com/wp-content/uploads/2015/11/12249800_10153820891439090_8007573611012789132_n.jpg When you think about an MBA program, usually the last thing you think of is professional collegiate sport. (Yes American’s I’m going...