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If AB/7 > 1/14 and A = B, which of the following must be gre
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Updated on: 19 Feb 2014, 02:52
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If AB/7 > 1/14 and A = B, which of the following must be greater than 1? A. A+B B. 1A C. 2A^2 D. A^2  1/2 E. A OA is C but It seems A also satisfies this condition...
I calculated it as below; AB/7 > 1/14 multiplying both sides by 14 2AB > 1 as A=B 2A^2 >1 and 2 B^2 > 1 Option (C) is true as per this logic While analyzing other options this is what I got... 2A^2>1 A^2>1/2 A>1/sqrt(2) as A=B, B >1/sqrt(2)
so A+B > 1/sqrt(2) + 1/sqrt(2) A+B > 2/sqrt(2) A+B > sqrt(2) This is also going to be greater than 1
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Originally posted by Conquistador22 on 19 Feb 2014, 01:10.
Last edited by Bunuel on 19 Feb 2014, 02:52, edited 1 time in total.
Renamed the topic and edited the question.




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Re: Inequalities MGMAT
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19 Feb 2014, 02:51
Conquistador22 wrote: This problem is from MGMAT Algebra Strategy Guide: If AB/7 > 1/14 and A=B While of the following must be greater than 1 ? a) A+B b) 1A c) 2A^2 d) A^21/2 e) A OA is C but It seems A also satisfies this condition...I calculated it as below; AB/7 > 1/14 multiplying both sides by 14 2AB > 1 as A=B 2A^2 >1 and 2 B^2 > 1 Option (C) is true as per this logic While analyzing other options this is what I got... 2A^2>1 A^2>1/2 A>1/sqrt(2)as A=B, B >1/sqrt(2) so A+B > 1/sqrt(2) + 1/sqrt(2) A+B > 2/sqrt(2) A+B > sqrt(2) This is also going to be greater than 1 If AB/7 > 1/14 and A = B, which of the following must be greater than 1? A. A+B B. 1A C. 2A^2 D. A^2  1/2 E. A First of all notice that the question asks which of the following MUST be true, not COULD be true. \(\frac{AB}{7} > \frac{1}{14}\) > \(2AB>1\). Since A = B, then \(2A^2>1\). Answer: C. As for option A: notice that from \(A^2>\frac{1}{2}\) it follows that A, and therefore B, since A = B, can be negative numbers, for example, 1, and in this case A + B = 2 < 1. The problem with your solution is that \(A^2>\frac{1}{2}\) means that \(A>\frac{1}{\sqrt{2}}\) OR \(A<\frac{1}{\sqrt{2}}\), not only \(A>\frac{1}{\sqrt{2}}\). Hope it's clear. P.S. Please read carefully and follow: rulesforpostingpleasereadthisbeforeposting133935.html Pay attention to rules 3, 5, and 7. Also, please hide the OA under the spoiler. Thank you.
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Re: Inequalities MGMAT
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19 Feb 2014, 04:01
Thanks Bunuel, Your explanation is awesome as usual. But I am a bit confused about below part. Bunuel wrote: The problem with your solution is that \(A^2>\frac{1}{2}\) means that \(A>\frac{1}{\sqrt{2}}\) OR \(A<\frac{1}{\sqrt{2}}\), not only \(A>\frac{1}{\sqrt{2}}\). . As per my understanding \(A^2>\frac{1}{2}\) means that \(A>+\frac{1}{\sqrt{2}}\) OR \(A>\frac{1}{\sqrt{2}}\). Could you please elaborate why \(A<\frac{1}{\sqrt{2}}\) ?



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Re: Inequalities MGMAT
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19 Feb 2014, 04:06
Conquistador22 wrote: Thanks Bunuel, Your explanation is awesome as usual. But I am a bit confused about below part. Bunuel wrote: The problem with your solution is that \(A^2>\frac{1}{2}\) means that \(A>\frac{1}{\sqrt{2}}\) OR \(A<\frac{1}{\sqrt{2}}\), not only \(A>\frac{1}{\sqrt{2}}\). . As per my understanding \(A^2>\frac{1}{2}\) means that \(A>+\frac{1}{\sqrt{2}}\) OR \(A>\frac{1}{\sqrt{2}}\). Could you please elaborate why \(A<\frac{1}{\sqrt{2}}\) ? Let me ask you a question: does \(x^2>4\) mean \(x>2\) or \(x>2\)? What does \(x>2\) or \(x>2\) even mean? \(x^2>4\) > \(x>2\) > \(x>2\) or \(x<2\). Go through the links below to brush up fundamentals on inequalities: Hope this helps.
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Re: Inequalities MGMAT
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19 Feb 2014, 06:56
Bunuel wrote: Let me ask you a question: does \(x^2>4\) mean \(x>2\) or \(x>2\)? What does \(x>2\) or \(x>2\) even mean?
\(x^2>4\) > \(x>2\) > \(x>2\) or \(x<2\).
This conclusion is based on below logic. \(x^2=25\) has TWO solutions, +5 and 5 so I thought \(x^2>4\) would also have two solutions +2 & 2, this is how I got \(x>2\) or \(x>2\) Could you please let me know why this is not valid ? I am asking very basic question but I know only after getting my basics clear, I will be able to get good score.... Thanks for bearing with me and my stupid questions .



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Re: Inequalities MGMAT
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19 Feb 2014, 07:03
Conquistador22 wrote: Bunuel wrote: Let me ask you a question: does \(x^2>4\) mean \(x>2\) or \(x>2\)? What does \(x>2\) or \(x>2\) even mean?
\(x^2>4\) > \(x>2\) > \(x>2\) or \(x<2\).
This conclusion is based on below logic. \(x^2=25\) has TWO solutions, +5 and 5 so I thought \(x^2>4\) would also have two solutions +2 & 2, this is how I got \(x>2\) or \(x>2\) Could you please let me know why this is not valid ? I am asking very basic question but I know only after getting my basics clear, I will be able to get good score.... Thanks for bearing with me and my stupid questions . Guess you did not follow the links I proposed... Again, what does x is more than 2 or x is more than 2 mean? What are the possible values of x in this case? For example, can x be 1, since it's more than 2? \(x^2>4\) indeed has two ranges, which are \(x>2\) or \(x<2\). Please follow the links in my previous post for more.
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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.
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If AB/7 > 1/14 and A = B, which of the following must be gre
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15 Nov 2014, 09:06
I don't understand, can someone please explain what I've done wrong?
\(\frac{AB}{7} > \frac{1}{14}\)
\(AB > \frac{7}{14}\)
\(AB > \frac{1}{2}\)
\(A^2 > \frac{1}{2}\)
\(\sqrt{A^2} > \sqrt{\frac{1}{2}}\)
\(A > \sqrt{\frac{1}{2}}\)
so it's either
\(A > \sqrt{\frac{1}{2}}\)
or
\(A < (\sqrt{\frac{1}{2}})\)
following this logic i find that answer C does not necessarily produce a number greater than 1, for example:
A=1/2
then:
2*(\(\frac{1}{2}^2\)) = 2*(\(\frac{1}{4}\)) = \(\frac{1}{2}\)
What have I done wrong? thank you in advance for your answer



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If AB/7 > 1/14 and A = B, which of the following must be gre
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15 Nov 2014, 09:49
pietropietro wrote: I don't understand, can someone please explain what I've done wrong?
\(\frac{AB}{7} > \frac{1}{14}\)
\(AB > \frac{7}{14}\)
\(AB > \frac{1}{2}\)
\(A^2 > \frac{1}{2}\)
\(\sqrt{A^2} > \sqrt{\frac{1}{2}}\)
\(A > \sqrt{\frac{1}{2}}\)
so it's either
\(A > \sqrt{\frac{1}{2}}\)
or
\(A < (\sqrt{\frac{1}{2}})\)
following this logic i find that answer C does not necessarily produce a number greater than 1, for example:
A=1/2
then:
2*(\(\frac{1}{2}^2\)) = 2*(\(\frac{1}{4}\)) = \(\frac{1}{2}\)
What have I done wrong? thank you in advance for your answer You picked A = 1/2. Is 1/2 less than sqrt(1/2)? In addition, does A = 1/2 satisfy the original condition?



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Re: If AB/7 > 1/14 and A = B, which of the following must be gre
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20 Nov 2014, 01:08
pietropietro wrote: I don't understand, can someone please explain what I've done wrong?
\(\frac{AB}{7} > \frac{1}{14}\)
\(AB > \frac{7}{14}\)
\(AB > \frac{1}{2}\)
\(A^2 > \frac{1}{2}\)
\(\sqrt{A^2} > \sqrt{\frac{1}{2}}\)
\(A > \sqrt{\frac{1}{2}}\)
so it's either
\(A > \sqrt{\frac{1}{2}}\)
or
\(A < (\sqrt{\frac{1}{2}})\)
following this logic i find that answer C does not necessarily produce a number greater than 1, for example:
A=1/2
then:
2*(\(\frac{1}{2}^2\)) = 2*(\(\frac{1}{4}\)) = \(\frac{1}{2}\)
What have I done wrong? thank you in advance for your answer There is no need to go along in simplification of the equation. Upto the step highlighted should be fine. Just place values in OA to get the answer
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Re: If AB/7 > 1/14 and A = B, which of the following must be gre
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23 Apr 2017, 22:46
Conquistador22 wrote: If AB/7 > 1/14 and A = B, which of the following must be greater than 1? A. A+B B. 1A C. 2A^2 D. A^2  1/2 E. A OA is C but It seems A also satisfies this condition...
I calculated it as below; AB/7 > 1/14 multiplying both sides by 14 2AB > 1 as A=B 2A^2 >1 and 2 B^2 > 1 Option (C) is true as per this logic While analyzing other options this is what I got... 2A^2>1 A^2>1/2 A>1/sqrt(2) as A=B, B >1/sqrt(2)
so A+B > 1/sqrt(2) + 1/sqrt(2) A+B > 2/sqrt(2) A+B > sqrt(2) This is also going to be greater than 1 The key to solving this problem is remembering to consider that although the product of A and B must be positive their individuals values can be negative a GMAT trap



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Re: If AB/7 > 1/14 and A = B, which of the following must be gre
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17 Jul 2018, 05:21
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Re: If AB/7 > 1/14 and A = B, which of the following must be gre &nbs
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