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:

If set N contains only consecutive positive integers, what is the sum of the numbers in set N? (1) Nineteen times the sum of the first number in the set and the last number in the set is 1729 (2) There are 38 numbers in the set.

I think i'll go with (C) on this one. Please allow me to explain.

So they are asking for the sum of the set of consecutive integers. We therefore need 2 things:

1) # of terms = Last - First + 1 2) Average of terms = (First + Last) / 2

Statement 1: We are given that 19 (F+L) = 1729 Then we can find F+L = 91. Hence, we can find the average.

Now can we find Last - First? I'm afraid this is not possible.

Statement 2: We are given the number of terms but we know nothing about the average of the terms. Hence Insuff

(1) and (2): Now we have everything to find the sum of the set. # of terms from Statement 2 Average from Statement 1. Voila

Re: If set N contains only consecutive positive integers, what [#permalink]

Show Tags

17 Dec 2013, 05:55

christoph wrote:

If set N contains only consecutive positive integers, what is the sum of the numbers in set N ?

(1) Nineteen times the sum of the first number in the set and the last number in the set is 1729 (2) There are 38 numbers in the set.

I was able to get the answer using A only , please tell me what I have done wrong

sum of n consecutive terms =( n/2)( F+L), where n is the number of terms , f = first term and L is the last term now can 19 be expressed as n/2 ? of course we can , so we can write 38/2(f+L) = 1729 --> 19(F+L)=1729 this is the exact expression for the sum of n consecutive integers , hence the number of terms is 38 and the sum is 1729

If set N contains only consecutive positive integers, what is the sum of the numbers in set N ?

(1) Nineteen times the sum of the first number in the set and the last number in the set is 1729 (2) There are 38 numbers in the set.

I was able to get the answer using A only , please tell me what I have done wrong

sum of n consecutive terms =( n/2)( F+L), where n is the number of terms , f = first term and L is the last term now can 19 be expressed as n/2 ? of course we can , so we can write 38/2(f+L) = 1729 --> 19(F+L)=1729 this is the exact expression for the sum of n consecutive integers , hence the number of terms is 38 and the sum is 1729

We need to find the sum of N consecutive integers. The sum = \(\frac{(first + last)}{2}*N\).

From (1) we have that \(19*(first + last) = 1729\) --> \((first + last) = 91\). So, we need to find the value of \(\frac{(first + last)}{2}*N = 91*\frac{N}{2}\). How can you find the value of this expression? You cannot! for example, N can be 2 (45, 46) and in this case the sum is 91, or N can be 90 (1, 2, ..., 90) and in this case the sum is 4095.

Re: If set N contains only consecutive positive integers, what [#permalink]

Show Tags

18 Dec 2013, 04:58

Bunuel wrote:

stne wrote:

christoph wrote:

If set N contains only consecutive positive integers, what is the sum of the numbers in set N ?

(1) Nineteen times the sum of the first number in the set and the last number in the set is 1729 (2) There are 38 numbers in the set.

I was able to get the answer using A only , please tell me what I have done wrong

sum of n consecutive terms =( n/2)( F+L), where n is the number of terms , f = first term and L is the last term now can 19 be expressed as n/2 ? of course we can , so we can write 38/2(f+L) = 1729 --> 19(F+L)=1729 this is the exact expression for the sum of n consecutive integers , hence the number of terms is 38 and the sum is 1729

We need to find the sum of N consecutive integers. The sum = \(\frac{(first + last)}{2}*N\).

From (1) we have that \(19*(first + last) = 1729\) --> \((first + last) = 91\). So, we need to find the value of \(\frac{(first + last)}{2}*N = 91*\frac{N}{2}\). How can you find the value of this expression? You cannot! for example, N can be 2 (45, 46) and in this case the sum is 91, or N can be 90 (1, 2, ..., 90) and in this case the sum is 4095.

Hope it helps.

Thank you for your reply.

I could be wrong again, most probably am but I am just trying to see the light and find out what is wrong with my logic

suppose I was told that (n/2)(F+L) = 1729 where n is the number of terms in a consecutive series and f is the first term and l is the last term , Then I could immediately say that the sum of these n consecutive terms is 1729, could I not?

now aren't we give the exact same thing indirectly? We are told 19(F+L)= 1729 which is the same as saying (38/2)(F+L)= 1729 so looking at this and comparing with (n/2)(F+L)= 1729

I was able to get the answer using A only , please tell me what I have done wrong

sum of n consecutive terms =( n/2)( F+L), where n is the number of terms , f = first term and L is the last term now can 19 be expressed as n/2 ? of course we can , so we can write 38/2(f+L) = 1729 --> 19(F+L)=1729 this is the exact expression for the sum of n consecutive integers , hence the number of terms is 38 and the sum is 1729

We need to find the sum of N consecutive integers. The sum = \(\frac{(first + last)}{2}*N\).

From (1) we have that \(19*(first + last) = 1729\) --> \((first + last) = 91\). So, we need to find the value of \(\frac{(first + last)}{2}*N = 91*\frac{N}{2}\). How can you find the value of this expression? You cannot! for example, N can be 2 (45, 46) and in this case the sum is 91, or N can be 90 (1, 2, ..., 90) and in this case the sum is 4095.

Hope it helps.

Thank you for your reply.

I could be wrong again, most probably am but I am just trying to see the light and find out what is wrong with my logic

suppose I was told that (n/2)(F+L) = 1729 where n is the number of terms in a consecutive series and f is the first term and l is the last term , Then I could immediately say that the sum of these n consecutive terms is 1729, could I not?

now aren't we give the exact same thing indirectly? We are told 19(F+L)= 1729 which is the same as saying (38/2)(F+L)= 1729 so looking at this and comparing with (n/2)(F+L)= 1729

why cannot I say n=38?

Suppose I tell you that the sum of the first and the last terms of n positive consecutive integers is 5. Can you find the sum of n consecutive integers?

The answer is NO. The set can be {2, 3} or {1, 2, 3, 4}. In the first case the sum is 5 and in the second case the sum is 10.
_________________

Re: If set N contains only consecutive positive integers, what [#permalink]

Show Tags

18 Dec 2013, 08:02

I agree , sum of first and last term is not enough to give the number of consecutive terms in a sequence but we are given more than that, we are given 19 * ( F +T) this immediately forced me to tell that there are 38 consecutive terms in the sequence .

because 19(F+T) can we written as 38/2(F+T) which can be compared to n/2(F+T) I know 19 can we written in other forms as well but our aim is to get it in the form n/2 where n is a integer.

If I was given 20 *(F+T) and we were dealing with consecutive terms then could I not tell there are 40 terms in the sequence, by changing eqn. to 40/2(F+L)?

So F+T = 1729/19 if we look at this form of the equation , then certainly this seems insufficient but after algebraic manipulation we get the equation in the form 19(F+T) = 1729 this form seems sufficient

I have learnt that in algebraic manipulation the same equation in certain form can give the answer well as in other forms it may not give the answer.

F+L = 1729/19 = insufficient but 19( F+T) = 1729 or (38/2) (F+L) = 1729 or (n/2)(F+L) is sufficient.

Is there a possibility that this could be a case here? Is there an issue of algebraic manipulation

Thank you for trying to make me understand.
_________________

I agree , sum of first and last term is not enough to give the number of consecutive terms in a sequence but we are given more than that, we are given 19 * ( F +T) this immediately forced me to tell that there are 38 consecutive terms in the sequence .

because 19(F+T) can we written as 38/2(F+T) which can be compared to n/2(F+T) I know 19 can we written in other forms as well but our aim is to get it in the form n/2 where n is a integer.

If I was given 20 *(F+T) and we were dealing with consecutive terms then could I not tell there are 40 terms in the sequence, by changing eqn. to 40/2(F+L)?

So F+T = 1729/19 if we look at this form of the equation , then certainly this seems insufficient but after algebraic manipulation we get the equation in the form 19(F+T) = 1729 this form seems sufficient

I have learnt that in algebraic manipulation the same equation in certain form can give the answer well as in other forms it may not give the answer.

F+L = 1729/19 = insufficient but 19( F+T) = 1729 or (38/2) (F+L) = 1729 or (n/2)(F+L) is sufficient.

Is there a possibility that this could be a case here? Is there an issue of algebraic manipulation

Thank you for trying to make me understand.

Again from (38/2) (F+L) = 1729 you cannot tell that n=38.
_________________

Re: If set N contains only consecutive positive integers, what [#permalink]

Show Tags

18 Dec 2013, 11:27

2

This post received KUDOS

Stne,

for the set {2,3} and {1,2,3,4} , if i were given 2* (F+T) = 10, as per you logic i can conclude there are 4 elements in the set. But that is not true as {2,3} can also be a set that satisfies 2* (F+T) = 10. The sum of {2,3} and {1,2,3,4} are different.

Re: If set N contains only consecutive positive integers, what [#permalink]

Show Tags

19 Dec 2013, 11:04

anjancgc wrote:

Stne,

for the set {2,3} and {1,2,3,4} , if i were given 2* (F+T) = 10, as per you logic i can conclude there are 4 elements in the set. But that is not true as {2,3} can also be a set that satisfies 2* (F+T) = 10. The sum of {2,3} and {1,2,3,4} are different.

Makes sense, you have managed to convince me.That's a wonderful first post by the way. +1 to you and also to Bunuel for his consistent assistance.
_________________

Re: If set N contains only consecutive positive integers, what [#permalink]

Show Tags

05 Jan 2016, 21:22

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.
_________________

If set N contains only consecutive positive integers, what [#permalink]

Show Tags

15 Jul 2016, 09:52

christoph wrote:

If set N contains only consecutive positive integers, what is the sum of the numbers in set N ?

(1) Nineteen times the sum of the first number in the set and the last number in the set is 1729 (2) There are 38 numbers in the set.

Statment 1) 19 (First+last)=1729 First + Last=1729/19=91 We don't know first and last digit InSufficient

(2) There are 38 numbers in the set Numbers can be anything (2,4,6,8,...........\(38^{th}\)term) or (120,122,124,.......38^{th} term) Insufficient

Merging both SUFFICIENT Here is the trick, most people don't know that If the total number of terms in a set containing even numbers is even then average of first and last term of set gives the average of the entire set. For example 2,4,6,8 standard way to find average= (2+4+6+8)/4=20/4= 5

The short cut method to find average is =(first+last)/2 ==> (2+8)/2= 5

This relationship hold true in case of even numbers having even terms So we now know that 19(f+l)=1729 f+l=91 (f+l) =91/2=40.5

thats tha average

To find the sum ;multiply it with the number of terms 38 * 40.5 = 1539

C is the answer
_________________

Posting an answer without an explanation is "GOD COMPLEX". The world doesn't need any more gods. Please explain you answers properly. FINAL GOODBYE :- 17th SEPTEMBER 2016. .. 16 March 2017 - I am back but for all purposes please consider me semi-retired.

gmatclubot

If set N contains only consecutive positive integers, what
[#permalink]
15 Jul 2016, 09:52

There’s something in Pacific North West that you cannot find anywhere else. The atmosphere and scenic nature are next to none, with mountains on one side and ocean on...

This month I got selected by Stanford GSB to be included in “Best & Brightest, Class of 2017” by Poets & Quants. Besides feeling honored for being part of...

Joe Navarro is an ex FBI agent who was a founding member of the FBI’s Behavioural Analysis Program. He was a body language expert who he used his ability to successfully...