GMAT Question of the Day - Daily to your Mailbox; hard ones only

It is currently 16 Oct 2018, 14:14

Close

GMAT Club Daily Prep

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.

Close

Request Expert Reply

Confirm Cancel

What is the 999th term of the series S ? (1) The first four terms of S

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

SVP
SVP
User avatar
V
Status: Preparing GMAT
Joined: 02 Nov 2016
Posts: 1722
Location: Pakistan
GPA: 3.39
Premium Member CAT Tests
What is the 999th term of the series S ? (1) The first four terms of S  [#permalink]

Show Tags

New post 06 Jan 2018, 14:22
00:00
A
B
C
D
E

Difficulty:

  55% (hard)

Question Stats:

42% (00:58) correct 58% (00:57) wrong based on 93 sessions

HideShow timer Statistics

What is the 999th term of the series S ?

(1) The first four terms of S are (1 + 1)^2, (2 + 1)^2, (3 + 1)^2, and (4 + 1)^2.
(2) For every x, the xth term of S is (x + 1)^2

_________________

Official PS Practice Questions
Press +1 Kudos if this post is helpful

PS Forum Moderator
avatar
D
Joined: 25 Feb 2013
Posts: 1218
Location: India
GPA: 3.82
GMAT ToolKit User Premium Member Reviews Badge
What is the 999th term of the series S ? (1) The first four terms of S  [#permalink]

Show Tags

New post 06 Jan 2018, 20:37
SajjadAhmad wrote:
What is the 999th term of the series S ?

(1) The first four terms of S are (1 + 1)^2, (2 + 1)^2, (3 + 1)^2, and (4 + 1)^2.
(2) For every x, the xth term of S is (x + 1)^2


Statement 1: we know the first \(4\) terms but what about terms after that? They could be anything. Hence insufficient

Statement 2: This clearly mentions the value of each term in the series.

So 999th term will be \((999+1)^2=1000^2\). Sufficient

Option B
Intern
Intern
avatar
B
Joined: 25 Mar 2017
Posts: 8
Re: What is the 999th term of the series S ? (1) The first four terms of S  [#permalink]

Show Tags

New post 16 Jan 2018, 11:11
Can someone explain why A as well cannot provide an answer?
The first four terms of the series are given and we are asked to find the 999th term. If we see a pattern in a series(and we know at least two terms), can we not find the nth term?

Or did I not get the question correctly?
DS Forum Moderator
avatar
P
Joined: 22 Aug 2013
Posts: 1348
Location: India
Premium Member
Re: What is the 999th term of the series S ? (1) The first four terms of S  [#permalink]

Show Tags

New post 16 Jan 2018, 11:23
1
NiruSinghal wrote:
Can someone explain why A as well cannot provide an answer?
The first four terms of the series are given and we are asked to find the 999th term. If we see a pattern in a series(and we know at least two terms), can we not find the nth term?

Or did I not get the question correctly?


Hi

First four terms are given. But there is no pattern given in the question. I know from the first four terms there seems to be a pattern, but we cannot conclude that just by looking at the first four terms.

Eg, If we are given first three terms of a series as 3, 5, 7... we cannot conclude that next term would be 9. It might be 11 (series of prime numbers) or the fourth term might just be 10 (so no pattern). A specific pattern is not necessary unless its specified in the question.

But the second statement generalises a pattern by specifying that x, the xth term of S is (x + 1)^2. So we can find the 999th term
Intern
Intern
avatar
B
Joined: 25 Mar 2017
Posts: 8
What is the 999th term of the series S ? (1) The first four terms of S  [#permalink]

Show Tags

New post 16 Jan 2018, 12:01
1
amanvermagmat wrote:
NiruSinghal wrote:
Can someone explain why A as well cannot provide an answer?
The first four terms of the series are given and we are asked to find the 999th term. If we see a pattern in a series(and we know at least two terms), can we not find the nth term?

Or did I not get the question correctly?


Hi

First four terms are given. But there is no pattern given in the question. I know from the first four terms there seems to be a pattern, but we cannot conclude that just by looking at the first four terms.

Eg, If we are given first three terms of a series as 3, 5, 7... we cannot conclude that next term would be 9. It might be 11 (series of prime numbers) or the fourth term might just be 10 (so no pattern). A specific pattern is not necessary unless its specified in the question.

But the second statement generalises a pattern by specifying that x, the xth term of S is (x + 1)^2. So we can find the 999th term



Thanks for the response :)

I understand it's not an arithmetic series but when I look at the terms, I do find a pattern:
2^2, 3^2, 4^2, 5^2. Can I assume that the xth term is (x+1)^2 ?

Also, if I expand the terms:
4, 9, 16, 25. the common difference increases by 2. And if we apply this pattern, the 5th term is 25+11=36, which is equal to 6^2(5+1)^2.

Just trying to understand where I'm going wrong.

TIA
DS Forum Moderator
avatar
P
Joined: 22 Aug 2013
Posts: 1348
Location: India
Premium Member
Re: What is the 999th term of the series S ? (1) The first four terms of S  [#permalink]

Show Tags

New post 16 Jan 2018, 23:00
1
NiruSinghal wrote:
amanvermagmat wrote:
NiruSinghal wrote:
Can someone explain why A as well cannot provide an answer?
The first four terms of the series are given and we are asked to find the 999th term. If we see a pattern in a series(and we know at least two terms), can we not find the nth term?

Or did I not get the question correctly?


Hi

First four terms are given. But there is no pattern given in the question. I know from the first four terms there seems to be a pattern, but we cannot conclude that just by looking at the first four terms.

Eg, If we are given first three terms of a series as 3, 5, 7... we cannot conclude that next term would be 9. It might be 11 (series of prime numbers) or the fourth term might just be 10 (so no pattern). A specific pattern is not necessary unless its specified in the question.

But the second statement generalises a pattern by specifying that x, the xth term of S is (x + 1)^2. So we can find the 999th term



Thanks for the response :)

I understand it's not an arithmetic series but when I look at the terms, I do find a pattern:
2^2, 3^2, 4^2, 5^2. Can I assume that the xth term is (x+1)^2 ?

Also, if I expand the terms:
4, 9, 16, 25. the common difference increases by 2. And if we apply this pattern, the 5th term is 25+11=36, which is equal to 6^2(5+1)^2.

Just trying to understand where I'm going wrong.

TIA


I understand where you are coming from. We have done those sort of questions. Given a series 1^2, 2^2, 3^2, 4^2.. then automatically the next thing which comes to mind is 5^2. It seems that there cannot be anything else, because from the first four terms, it seems that the pattern for each term is n^2.

But since this is a GMAT data sufficiency question, we cannot assume that would be the case. Its possible that i decide to make a series where the first four terms follow the rule n^2, next four terms follow (n+1)^2, next four terms follow (n+2)^2 and so on.. In that case the series will look like this:
1, 4, 9, 16, 36, 49, 64, 81, 121, 144,...

So how do we know that the given series (as per first statement) is not something like this. How do we know that ALL terms will follow n^2 or (n+1)^2?
That is what is specified only in second statement.
Intern
Intern
avatar
B
Joined: 25 Mar 2017
Posts: 8
Re: What is the 999th term of the series S ? (1) The first four terms of S  [#permalink]

Show Tags

New post 16 Jan 2018, 23:28
1
I understand where you are coming from. We have done those sort of questions. Given a series 1^2, 2^2, 3^2, 4^2.. then automatically the next thing which comes to mind is 5^2. It seems that there cannot be anything else, because from the first four terms, it seems that the pattern for each term is n^2.

But since this is a GMAT data sufficiency question, we cannot assume that would be the case. Its possible that i decide to make a series where the first four terms follow the rule n^2, next four terms follow (n+1)^2, next four terms follow (n+2)^2 and so on.. In that case the series will look like this:
1, 4, 9, 16, 36, 49, 64, 81, 121, 144,...

So how do we know that the given series (as per first statement) is not something like this. How do we know that ALL terms will follow n^2 or (n+1)^2?
That is what is specified only in second statement.[/quote]


Thanks, Aman.

Indeed, it's one of those lessons learned in school to assume based on the first few terms.
Will keep this in mind, thanks again :)
GMAT Club Bot
Re: What is the 999th term of the series S ? (1) The first four terms of S &nbs [#permalink] 16 Jan 2018, 23:28
Display posts from previous: Sort by

What is the 999th term of the series S ? (1) The first four terms of S

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  


Copyright

GMAT Club MBA Forum Home| About| Terms and Conditions and Privacy Policy| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.