Author 
Message 
TAGS:

Hide Tags

Manager
Joined: 16 Feb 2010
Posts: 188

Sequence S consists of 24 nonzero integers. If each term in
[#permalink]
Show Tags
Updated on: 04 Jun 2013, 04:55
Question Stats:
40% (01:26) correct 60% (01:34) wrong based on 787 sessions
HideShow timer Statistics
Sequence S consists of 24 nonzero integers. If each term in S after the second is the product of the previous two terms, how many terms in S are negative? (1) The third term in S is positive (2) The fourth term in S is negative The book claims this is one of the most diff questions GMAT can produce which I believe it is a joke....nevertheless got it wrong because I misinterpreted the question. I am posting to see if more people will misinterpret or if it is just me that is going *o*kers
Official Answer and Stats are available only to registered users. Register/ Login.
Originally posted by zisis on 07 Aug 2010, 12:34.
Last edited by Bunuel on 04 Jun 2013, 04:55, edited 2 times in total.
Edited the question and added the OA.




Math Expert
Joined: 02 Sep 2009
Posts: 48037

Re: Kaplan "800" DS: seq
[#permalink]
Show Tags
07 Aug 2010, 13:17
zisis wrote: Sequence S consists of 24 nonzero integers. If each term in S after the second is the product of the previous two terms, how many terms in S are negative?
(1) The third term in S is negative (2) The fourth term in S is positive
The book claims this is one of the most diff questions GMAT can produce which I believe it is a joke....nevertheless got it wrong because I misinterpreted the question. I am posting to see if more people will misinterpret or if it is just me that is going *o*kers Answer cannot be B, it should be A.
Sequence S consists of 24 nonzero integers. If each term in S after the second is the product of the previous two terms, how many terms in S are negative?
(1) The third term in S is negative > first and second terms must have opposite signs so we can hve following two scenarios:
++++... OR: ++++...
You can see that in both cases there is a repeated pattern of three terms in which 2 are negative and 1 positive (+ or +) so in both cases out of 24 terms 2/3 will be negative, so there will be 16 negative terms. Sufficient.
(2) The fourth term in S is positive > either all terms are positive, so zero negatives or ++... and not all terms are positive, so more than zero negatives. Not sufficient.
Answer: A. If the OA is B then it should be:Sequence S consists of 24 nonzero integers. If each term in S after the second is the product of the previous two terms, how many terms in S are negative?(1) The third term in S is positive > either all terms are positive, so zero negatives or +... and not all terms are positive, so more than zero negatives. Not sufficient. (2) The fourth term in S is negative > again two cases: +++...OR +++...The same here: in both cases there is a repeated pattern of three terms in which 2 are negative and 1 positive (+ or +) so in both cases out of 24 terms 2/3 will be negative, so there will be 16 negative terms. Sufficient. Answer: B. Hope it's clear.
_________________
New to the Math Forum? Please read this: Ultimate GMAT Quantitative Megathread  All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics




Manager
Joined: 16 Feb 2010
Posts: 188

Re: Kaplan "800" DS: seq
[#permalink]
Show Tags
07 Aug 2010, 13:37
the OA is def the one posted....double checked it..... will let more people get involved and then post the OA explanation.....your post supports my view that this question is not phrased correclt (ie is open to misinterpetation)..... the bigger question is how can we make sure that the practise we get is up to the test's standard if massive companies like Kaplan cannt phrase their questions correctly....



Math Expert
Joined: 02 Sep 2009
Posts: 48037

Re: Kaplan "800" DS: seq
[#permalink]
Show Tags
07 Aug 2010, 13:45



Manager
Joined: 16 Feb 2010
Posts: 188

Re: Kaplan "800" DS: seq
[#permalink]
Show Tags
07 Aug 2010, 14:06
you were right......I AM going mental.... just edited my post....hope this makes more sense



Manager
Joined: 16 Feb 2010
Posts: 188

Re: Kaplan "800" DS: seq
[#permalink]
Show Tags
08 Aug 2010, 03:29
zisis wrote: Sequence S consists of 24 nonzero integers. If each term in S after the second is the product of the previous two terms, how many terms in S are negative?
(1) The third term in S is positive (2) The fourth term in S is negative
The book claims this is one of the most diff questions GMAT can produce which I believe it is a joke....nevertheless got it wrong because I misinterpreted the question. I am posting to see if more people will misinterpret or if it is just me that is going *o*kers One final question: I misinterpreted the If each term in S after the second part....thought that the "formula"/instructions (\(An= An1 * An2\) is only for the third onwards, thus we know nothing for the first two terms thus it is not possible to answer the question.....is that a valid conclusion....?



Math Expert
Joined: 02 Sep 2009
Posts: 48037

Re: Kaplan "800" DS: seq
[#permalink]
Show Tags
08 Aug 2010, 03:51
zisis wrote: zisis wrote: Sequence S consists of 24 nonzero integers. If each term in S after the second is the product of the previous two terms, how many terms in S are negative?
(1) The third term in S is positive (2) The fourth term in S is negative
The book claims this is one of the most diff questions GMAT can produce which I believe it is a joke....nevertheless got it wrong because I misinterpreted the question. I am posting to see if more people will misinterpret or if it is just me that is going *o*kers One final question: I misinterpreted the If each term in S after the second part....thought that the "formula"/instructions (\(An= An1 * An2\) is only for the third onwards, thus we know nothing for the first two terms thus it is not possible to answer the question.....is that a valid conclusion....? You interpreted correctly: \(a_n=a_{n1}*a_{n2}\), for \(n>2\). But you are not right about the first two terms for the following statements: (2) The fourth term in S is negative > \(a_4=negative=a_3*a_2\) > second and third term must have opposite signs, so third term is either positive or negative. Now, case 1: if third term is positive then first and second terms must be both negative (for first and second it's not possible to be both positive as in this case fourth term would be positive too and we know that it's negative) and case 2: if third term is negative then first and second terms must have opposite signs. So there are only 2 cases possible: +++...OR +++...In both cases there is a repeated pattern of three terms in which 2 are negative and 1 positive (+ or +) so in both cases out of 24 terms 2/3 will be negative, so there will be 16 negative terms. Sufficient. Answer: B.
_________________
New to the Math Forum? Please read this: Ultimate GMAT Quantitative Megathread  All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics



Intern
Joined: 05 Nov 2009
Posts: 29

Re: Kaplan "800" DS: seq
[#permalink]
Show Tags
08 Aug 2010, 17:25
I also get B. You can establish a pattern at 4 and each combination to get negative ( * + or + * ) gets to the same number of negative numbers. I must admist that I did this the long way, without a formula  prorbably took a little over 2 minutes.



Senior Manager
Joined: 21 Mar 2010
Posts: 286

Re: DS Question Kaplan 800
[#permalink]
Show Tags
24 Feb 2011, 22:59
rajeshaaidu wrote: No clue! It's really tough one. Please give official explanation. A) and D) I have eliminated but I was confused between B) and C) because I was not able to explain stmtB. If you write out the options resulting from b T3 below will be T1T2 T1  T2 T3T4 ve ve +ve ve ve +ve ve ve For both these cases expand out the first 8 terms and you will see the ratio of 2:1 for negative to positive!



Retired Moderator
Joined: 20 Dec 2010
Posts: 1877

Re: DS Question Kaplan 800
[#permalink]
Show Tags
24 Feb 2011, 23:39
I classify these types of questions as torturous; because we need to count them out to be sure. 1. We can easily rule this out because the 3rd term is +ve; first two can either be ve or all can be positive. Not sufficient. 2. This statement is little hairy. X\(++++++++\). 16 ves Y\(++++++++\). 16 ves Sufficient. Well after some thought; you may recognize the pattern that there are two negatives after every +ve; but I would rather write them all out and count them. As you see for X; first position is ve and the 2nd +ve. 3rd and 4th are negative and 5th +ve and the pattern continues. You may now count ves. Likewise for Y. Ans: "B"
_________________
~fluke
GMAT Club Premium Membership  big benefits and savings



Director
Status: Impossible is not a fact. It's an opinion. It's a dare. Impossible is nothing.
Affiliations: University of Chicago Booth School of Business
Joined: 03 Feb 2011
Posts: 787

Re: Kaplan "800" DS: seq
[#permalink]
Show Tags
25 Feb 2011, 11:18
Bunuel you are awesome ! If I had seen this question on test day I would have marked C and move on ! But then I took numbers and yes it answered. So  its imperative to find the first negative term. That is the key for the pattern ? Right?



Math Expert
Joined: 02 Sep 2009
Posts: 48037

Re: Sequence S consists of 24 nonzero integers. If each term in
[#permalink]
Show Tags
04 Jun 2013, 05:03



Manager
Joined: 28 Feb 2012
Posts: 112
Concentration: Strategy, International Business
GPA: 3.9
WE: Marketing (Other)

Re: Sequence S consists of 24 nonzero integers. If each term in
[#permalink]
Show Tags
05 Jun 2013, 03:25
Sequence S consists of 24 nonzero integers. If each term in S after the second is the product of the previous two terms, how many terms in S are negative? (1) The third term in S is positive (2) The fourth term in S is negative One important thing to understand is that in GMAT sequence questions there is almost always a pattern. So there is no real need to calculate all 24 integers' signs. The most difficult part in this question is: If each term in S after the second is the product of the previous two terms . It is the same as saying that: x; y; xy; x(y^2); (x^2)(y^3); (x^3)(y^5); (x^5)(y^8); ... 1 st.) xy is positive. In this case both x and y are negative or they both positive. If both positive all the terms will be positive: (+) (+) (+) (+) (+) (+)... In case both are negative we have: () () (+) () () () (+).... Two different answers  statement is not sufficient 2 st.) x(y^2) is negative. There are two possible options: x is negative and y is positive, or x is negative and y is negative. In the 1st option we have the following pattern: () (+) () () (+) () () (+)... In the 2nd option we have the follwing pattern: () () (+) () () (+) () ()... It starts slightly different but the pattern is the same, so we can conclude that the number of positives and negatives within 24 integers will be the same rerdless of the options. So the answer is B.
_________________
If you found my post useful and/or interesting  you are welcome to give kudos!



Manager
Joined: 07 Apr 2012
Posts: 105
Location: United States
Concentration: Entrepreneurship, Operations
GPA: 3.9
WE: Operations (Manufacturing)

Re: Sequence S consists of 24 nonzero integers. If each term in
[#permalink]
Show Tags
04 Sep 2013, 02:42
Even though OA is B and is right, # of negative terms is 17 and not 16. The first term has to be negative in both the scenarios of B.



Math Expert
Joined: 02 Sep 2009
Posts: 48037

Re: Sequence S consists of 24 nonzero integers. If each term in
[#permalink]
Show Tags
04 Sep 2013, 03:41



Manager
Joined: 07 Apr 2012
Posts: 105
Location: United States
Concentration: Entrepreneurship, Operations
GPA: 3.9
WE: Operations (Manufacturing)

Re: Sequence S consists of 24 nonzero integers. If each term in
[#permalink]
Show Tags
04 Sep 2013, 04:22
Bunuel wrote: ygdrasil24 wrote: Even though OA is B and is right, # of negative terms is 17 and not 16. The first term has to be negative in both the scenarios of B. There are 24 numbers and 2/3 are negative, thus 16 numbers are negative not 17. Yes 16, I over worked on the final answer



Intern
Joined: 13 Apr 2014
Posts: 12

Re: Sequence S consists of 24 nonzero integers. If each term in
[#permalink]
Show Tags
15 Apr 2014, 05:24
Sequence S consists of 24 nonzero integers. If each term in S after the second is the product of the previous two terms, how many terms in S are negative? (1) The third term in S is positive > either all terms are positive, so zero negatives or +... and not all terms are positive, so more than zero negatives. Not sufficient. (2) The fourth term in S is negative > again two cases: +++... OR +++... The same here: in both cases there is a repeated pattern of three terms in which 2 are negative and 1 positive (+ or +) so in both cases out of 24 terms 2/3 will be negative, so there will be 16 negative terms. Sufficient. Answer: B. tnx for this
_________________
http://www.gmatacademy.ir best for iranian



Intern
Joined: 08 Jan 2014
Posts: 19
Location: United States
Concentration: General Management, Entrepreneurship
GMAT Date: 06302014
GPA: 3.99
WE: Analyst (Consulting)

Re: Sequence S consists of 24 nonzero integers. If each term in
[#permalink]
Show Tags
10 May 2014, 12:11
1st term x 2nd term y S={x,y,xy,xy^2.........}
since 4th term is ve , xY^2 is ve i.e. x is ve since y^2 cannot be ve. Now since 1st term is ve there can be 2 different pattern for the sequence assuming 2nd term to be either +ve or ve.
S={,,+,,,+,......} or S={,+,,,+,,......}
So its clear that either 2nd term is +ve or Ve the # of ve terms is equal for 24 terms(since # of terms is a product of 3).



Intern
Joined: 20 May 2014
Posts: 32

Re: Sequence S consists of 24 nonzero integers. If each term in
[#permalink]
Show Tags
07 Jul 2014, 09:30
ziko wrote: Sequence S consists of 24 nonzero integers. If each term in S after the second is the product of the previous two terms, how many terms in S are negative?
(1) The third term in S is positive (2) The fourth term in S is negative
One important thing to understand is that in GMAT sequence questions there is almost always a pattern. So there is no real need to calculate all 24 integers' signs. The most difficult part in this question is: If each term in S after the second is the product of the previous two terms .
It is the same as saying that: x; y; xy; x(y^2); (x^2)(y^3); (x^3)(y^5); (x^5)(y^8); ...
1 st.) xy is positive. In this case both x and y are negative or they both positive. If both positive all the terms will be positive: (+) (+) (+) (+) (+) (+)... In case both are negative we have: () () (+) () () () (+).... Two different answers  statement is not sufficient
2 st.) x(y^2) is negative. There are two possible options: x is negative and y is positive, or x is negative and y is negative. In the 1st option we have the following pattern: () (+) () () (+) () () (+)... In the 2nd option we have the follwing pattern: () () (+) () () (+) () ()... It starts slightly different but the pattern is the same, so we can conclude that the number of positives and negatives within 24 integers will be the same rerdless of the options. So the answer is B. Why isn't fourth term x^2y^2



Math Expert
Joined: 02 Sep 2009
Posts: 48037

Re: Sequence S consists of 24 nonzero integers. If each term in
[#permalink]
Show Tags
07 Jul 2014, 09:35
sagnik2422 wrote: ziko wrote: Sequence S consists of 24 nonzero integers. If each term in S after the second is the product of the previous two terms, how many terms in S are negative?
(1) The third term in S is positive (2) The fourth term in S is negative
One important thing to understand is that in GMAT sequence questions there is almost always a pattern. So there is no real need to calculate all 24 integers' signs. The most difficult part in this question is: If each term in S after the second is the product of the previous two terms .
It is the same as saying that: x; y; xy; x(y^2); (x^2)(y^3); (x^3)(y^5); (x^5)(y^8); ...
1 st.) xy is positive. In this case both x and y are negative or they both positive. If both positive all the terms will be positive: (+) (+) (+) (+) (+) (+)... In case both are negative we have: () () (+) () () () (+).... Two different answers  statement is not sufficient
2 st.) x(y^2) is negative. There are two possible options: x is negative and y is positive, or x is negative and y is negative. In the 1st option we have the following pattern: () (+) () () (+) () () (+)... In the 2nd option we have the follwing pattern: () () (+) () () (+) () ()... It starts slightly different but the pattern is the same, so we can conclude that the number of positives and negatives within 24 integers will be the same rerdless of the options. So the answer is B. Why isn't fourth term x^2y^2 Each term in S after the second is the product of the previous two terms. x y xy y*xy = xy^2 xy*xy^2 = x^2y^3 ... Hope it's clear now.
_________________
New to the Math Forum? Please read this: Ultimate GMAT Quantitative Megathread  All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics




Re: Sequence S consists of 24 nonzero integers. If each term in &nbs
[#permalink]
07 Jul 2014, 09:35



Go to page
1 2
Next
[ 22 posts ]



