Author 
Message 
TAGS:

Hide Tags

Manager
Status: Bell the GMAT!!!
Affiliations: Aidha
Joined: 16 Aug 2011
Posts: 154
Location: Singapore
Concentration: Finance, General Management
GMAT 1: 680 Q46 V37 GMAT 2: 620 Q49 V27 GMAT 3: 700 Q49 V36
WE: Other (Other)

Is x^1/2 a prime number? [#permalink]
Show Tags
Updated on: 11 Jul 2013, 01:50
Question Stats:
53% (01:15) correct 47% (01:11) wrong based on 274 sessions
HideShow timer Statistics
Is ￼x^1/2 a prime number? (1) 3x  7 = 2x + 2 (2) ￼x^2 = 9x
Official Answer and Stats are available only to registered users. Register/ Login.
_________________
If my post did a dance in your mind, send me the steps through kudos :)
My MBA journey at http://mbadilemma.wordpress.com/
Originally posted by GMATmission on 24 Aug 2011, 23:41.
Last edited by Bunuel on 11 Jul 2013, 01:50, edited 1 time in total.
Renamed the topic, edited the question and added the OA.



Manager
Joined: 30 Sep 2009
Posts: 106

Re: number properties [#permalink]
Show Tags
25 Aug 2011, 00:05
the answer is C
1 3x7=2x+2
> (3x7)=2x+2 on solving this we get x=1 > +(3x7)=2x+2 on solving this we get x=9 so insufficient
B ) x^2=9x x^29x=0 x(x9)=0 hence x=0,9 insuff
combining both will give x=9 hence sqroot(9) will give 3 which is a prime number



Manager
Joined: 19 Jul 2011
Posts: 94
Concentration: Finance, Economics
GPA: 3.9

Re: number properties [#permalink]
Show Tags
25 Aug 2011, 04:28
(1) ￼mod (3x7) = 2x+2 3x7=2x+2 x=9 3x+7=2x+2 x=1 x can be 9 or 1, 9^1/2 is 3 (prime) while 1^1/2 is 1 (not prime) INSUFFICIENT (2) ￼x^2 = 9x x(x9)=0 x can only have two solutions 0 or 9 INSUFFICIENT But combining the two statements we have 9 in both so the answer is 9 9^1/2 = 3, which is prime So the answer is C
_________________
Show Thanks to fellow members with Kudos its shows your appreciation and its free



Manager
Status: Bell the GMAT!!!
Affiliations: Aidha
Joined: 16 Aug 2011
Posts: 154
Location: Singapore
Concentration: Finance, General Management
GMAT 1: 680 Q46 V37 GMAT 2: 620 Q49 V27 GMAT 3: 700 Q49 V36
WE: Other (Other)

Re: number properties [#permalink]
Show Tags
26 Aug 2011, 08:45
abhi398 wrote: the answer is C
1 3x7=2x+2
> (3x7)=2x+2 on solving this we get x=1 > +(3x7)=2x+2 on solving this we get x=9 so insufficient
B ) x^2=9x x^29x=0 x(x9)=0 hence x=0,9 insuff
combining both will give x=9 hence sqroot(9) will give 3 which is a prime number OA is C. I was wondering whether we should consider negative values. Sq root of 9 = +/3. +3 is prime and 3 is not. What do you say?
_________________
If my post did a dance in your mind, send me the steps through kudos :)
My MBA journey at http://mbadilemma.wordpress.com/



Manager
Joined: 19 Jul 2011
Posts: 94
Concentration: Finance, Economics
GPA: 3.9

Re: number properties [#permalink]
Show Tags
26 Aug 2011, 09:15
When we take the square root of a number in the GMAT the answer is always positive.
_________________
Show Thanks to fellow members with Kudos its shows your appreciation and its free



Director
Joined: 03 May 2007
Posts: 832
Schools: University of Chicago, Wharton School

Re: number properties [#permalink]
Show Tags
27 Aug 2011, 14:42
GMATmission wrote: OA is C. I was wondering whether we should consider negative values. Sq root of 9 = +/3. +3 is prime and 3 is not. What do you say? nammers wrote: When we take the square root of a number in the GMAT the answer is always positive. x has 2 roots i.e. sqrt(x) and  sqrt(x). The question is asking about positive root i.e. sqrt(x). so sqrt(x) has always a +ve value. Similarly sqrt(9) = 3. sqrt(9) = 3.



Manager
Joined: 10 Mar 2014
Posts: 212

Re: Is x^1/2 a prime number? [#permalink]
Show Tags
10 Jul 2014, 01:40
GMATmission wrote: Is ￼x^1/2 a prime number?
(1) 3x  7 = 2x + 2 (2) ￼x^2 = 9x Hi Bunnel, Could you please provide your comments on this? I am using following logic 3x7 = 2x +2. here L.H.S is positive so 2x+2 >= 0> 2x>=2> x>=1 so if if x>= 1 then 3x7 = 3x+7 = 2x+2 5x = 5 x = 1 only 1 value so sufficient. Ans A ( my question is why we are considering other scenario to get 9) in st2 x^2 = 9x x^29x = 0 x(x9) = 0 x= 0 or 9 here we are getting 2 values so not sufficient.



Math Expert
Joined: 02 Sep 2009
Posts: 46991

Re: Is x^1/2 a prime number? [#permalink]
Show Tags
10 Jul 2014, 02:04



Manager
Joined: 10 Mar 2014
Posts: 212

Re: Is x^1/2 a prime number? [#permalink]
Show Tags
10 Jul 2014, 03:14
Bunuel wrote: PathFinder007 wrote: GMATmission wrote: Is ￼x^1/2 a prime number?
(1) 3x  7 = 2x + 2 (2) ￼x^2 = 9x Hi Bunnel, Could you please provide your comments on this? I am using following logic 3x7 = 2x +2. here L.H.S is positive so 2x+2 >= 0> 2x>=2> x>=1 so if if x>= 1 then 3x7 = 3x+7 = 2x+2 5x = 5 x = 1 only 1 value so sufficient. Ans A ( my question is why we are considering other scenario to get 9) in st2 x^2 = 9x x^29x = 0 x(x9) = 0 x= 0 or 9 here we are getting 2 values so not sufficient. 2 questions: 1. Does x=9 satisfy the equation? 2. Why do you say that when x>=1, then 3x7 = (3x7)? Hi Bunnel, 1. Yes x=9 satisfy the equation. 2. I told x>= 1 because in st1 it is given that 3x7 = 2x+2. Here LHS. is in modulus so it is >=0. so RHS should be >=0 2x+2>= 0 > 2x>=2>x>=1 Thanks



Math Expert
Joined: 02 Sep 2009
Posts: 46991

Is x^1/2 a prime number? [#permalink]
Show Tags
10 Jul 2014, 03:56
PathFinder007 wrote: Bunuel wrote: PathFinder007 wrote: Hi Bunnel,
Could you please provide your comments on this?
I am using following logic
3x7 = 2x +2. here L.H.S is positive so 2x+2 >= 0> 2x>=2> x>=1
so if if x>= 1 then 3x7 = 3x+7 = 2x+2
5x = 5 x = 1
only 1 value so sufficient. Ans A ( my question is why we are considering other scenario to get 9)
in st2
x^2 = 9x x^29x = 0 x(x9) = 0 x= 0 or 9
here we are getting 2 values so not sufficient. 2 questions: 1. Does x=9 satisfy the equation? 2. Why do you say that when x>=1, then 3x7 = (3x7)? Hi Bunnel, 1. Yes x=9 satisfy the equation. 2. I told x>= 1 because in st1 it is given that 3x7 = 2x+2. Here LHS. is in modulus so it is >=0. so RHS should be >=0 2x+2>= 0 > 2x>=2>x>=1 Thanks You did not understand my second question. Yes, from (1) x>=1 BUT why does that mean that 3x7 = (3x7)? P.S. It's Bunuel not Bunnel.
_________________
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: 10 Mar 2014
Posts: 212

Re: Is x^1/2 a prime number? [#permalink]
Show Tags
10 Jul 2014, 06:07
Hey Bunuel I know I was using Bunnel bcz in my area where I live in india its mean wise. So I used this word for you.
i think i got confusion here 3x7 = (3x7) as i thought putting 1 makes it negative in modulus 37 . but I think this is not the case and it should be 3x7 = 3x7.
Thanks Bunuel for all your replies. Please clarify this



Math Expert
Joined: 02 Sep 2009
Posts: 46991

Re: Is x^1/2 a prime number? [#permalink]
Show Tags
10 Jul 2014, 12:30



Manager
Joined: 05 Jun 2014
Posts: 63

Is x^1/2 a prime number? [#permalink]
Show Tags
01 Sep 2014, 03:25
Hey bunuel, In Manhattan gmat book its written that absolute values have +ve or ve value. For +ve value the sign after solving is positive then its a correct soln, same goes for ve. But here when we solve for +ve value we get +9, thats a correct soln, but for ve soln we get +1, which isnt negative, so its not a legitimte soln and hence should be ignored, acc to MGMAT. Plz help !



Math Expert
Joined: 02 Sep 2009
Posts: 46991

Re: Is x^1/2 a prime number? [#permalink]
Show Tags
01 Sep 2014, 03:35
sunaimshadmani wrote: Hey bunuel, In Manhattan gmat book its written that absolute values have +ve or ve value. For +ve value the sign after solving is positive then its a correct soln, same goes for ve. But here when we solve for +ve value we get +9, thats a correct soln, but for ve soln we get +1, which isnt negative, so its not a legitimte soln and hence should be ignored, acc to MGMAT. Plz help ! Not sure I understand what you mean there. As for the roots of 3x  7 = 2x + 2: both x = 1 and x = 9 satisfy this equation, thus both are valid solutions. Maybe if you could show your work, I'd be able to say more.
_________________
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 Feb 2014
Posts: 15
Location: India
Concentration: Human Resources, General Management
GPA: 3.33

Re: Is x^1/2 a prime number? [#permalink]
Show Tags
06 Sep 2014, 11:05
abhi398 wrote: the answer is C
1 3x7=2x+2
> (3x7)=2x+2 on solving this we get x=1 > +(3x7)=2x+2 on solving this we get x=9 so insufficient
B ) x^2=9x x^29x=0 x(x9)=0 hence x=0,9 insuff
combining both will give x=9 hence sqroot(9) will give 3 which is a prime number why cant we take x^2=9x as x.x=9.x so x on both sides get cancelled hence x=9



NonHuman User
Joined: 09 Sep 2013
Posts: 7241

Re: Is x^1/2 a prime number? [#permalink]
Show Tags
25 Nov 2017, 13:04
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.
_________________
GMAT Books  GMAT Club Tests  Best Prices on GMAT Courses  GMAT Mobile App  Math Resources  Verbal Resources




Re: Is x^1/2 a prime number?
[#permalink]
25 Nov 2017, 13:04






