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What is the value of a  b? (1) a = b + 4 (2) (a  b)^2 = 1
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Updated on: 31 Oct 2018, 08:50
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So I ran across this question in the GMAT paper exams: What is the value of a  b? (1) \(a = b + 4\) (2) \((a  b)^2 = 16\) I marked D since I thought that the GMAT only considers square roots of numbers to equal the positive root only and not the negative root. Thus, wouldn't (2) above be equivalent to a  b = 4? Can someone please explain to me how the GMAT treats square roots of numbers? Thanks!
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Originally posted by rk9 on 30 Aug 2010, 13:52.
Last edited by carcass on 31 Oct 2018, 08:50, edited 1 time in total.
Edited by Carcass




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Re: What is the value of a  b? (1) a = b + 4 (2) (a  b)^2 = 1
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30 Aug 2010, 14:06
rk9 wrote: So I ran across this question in the GMAT paper exams:
What is the value of a  b?
(1) a = b + 4 (2) (a  b)^2 = 16
I marked D since I thought that the GMAT only considers square roots of numbers to equal the positive root only and not the negative root. Thus, wouldn't (2) above be equivalent to a  b = 4? Can someone please explain to me how the GMAT treats square roots of numbers? Thanks! Hi, and welcome to Gmat Club! It seems that you are mixing square roots (\(\sqrt{x}\)) with quadratics (\(x^2\)). When the GMAT provides the square root sign for an even root, such as \(\sqrt{x}\) or \(\sqrt[4]{x}\), then the only accepted answer is the positive root. That is, \(\sqrt{25}=5\), NOT +5 or 5. Even roots have only nonnegative value on the GMAT. Odd roots will have the same sign as the base of the root. For example, \(\sqrt[3]{125} =5\) and \(\sqrt[3]{64} =4\). In contrast, the equation \(x^2=25\) has TWO solutions, +5 and 5. Hope it helps.
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Re: What is the value of a  b? (1) a = b + 4 (2) (a  b)^2 = 1
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30 Aug 2010, 14:08
rk9 wrote: So I ran across this question in the GMAT paper exams:
What is the value of a  b?
(1) a = b + 4 (2) (a  b)^2 = 16
I marked D since I thought that the GMAT only considers square roots of numbers to equal the positive root only and not the negative root. Thus, wouldn't (2) above be equivalent to a  b = 4? Can someone please explain to me how the GMAT treats square roots of numbers? Thanks! You are right +ve square roots are there. But when you will take square root on both the sides, how you will come to know whether a>b or b>a (a  b)^2 = 16 take square root on both the sides => ab = 4 , see both the square roots are positive. Now when you will open the modulus you will have to consider two cases. a>b and b>a if a>b then a  b = 4 if b>a then a  b = 4. Hope this helps
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Re: What is the value of a  b? (1) a = b + 4 (2) (a  b)^2 = 1
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30 Aug 2010, 15:25
Thank you both! This helps!



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Re: What is the value of a  b? (1) a = b + 4 (2) (a  b)^2 = 1
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21 Sep 2010, 10:00
hey Gurpreet Bunuel ....thanx so much I was struggling at this.. even I was mixing quadratic and roots ..... ( in what proportion it does not matter )...cheers
By the way why dont guys open an academy ...with the name as " We make duds  STUDS in no time.. example gauravnagpal."
LOL !!! lets keep enjoying the journey ..
cheers



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Re: What is the value of a  b? (1) a = b + 4 (2) (a  b)^2 = 1
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21 Sep 2010, 10:44
1) Sufficient 2) ab = 4 or 4 > insufficient Ans is A
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Re: What is the value of a  b? (1) a = b + 4 (2) (a  b)^2 = 1
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01 Dec 2014, 07:07
Algebra DS problem Asking ab =? Value based !! 1, Easy to get ab = 4 2, Formula ( ab)^2 = 16 Even after solving this we cannot get ab? So No answer A
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Re: What is the value of a  b? (1) a = b + 4 (2) (a  b)^2 = 1
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05 Jul 2016, 00:13
[quote="rk9"]So I ran across this question in the GMAT paper exams:
What is the value of a  b?
(1) a = b + 4 (2) (a  b)^2 = 16
I marked D since I thought that the GMAT only considers square roots of numbers to equal the positive root only and not the negative root. Thus, wouldn't (2) above be equivalent to a  b = 4? Can someone please explain to me how the GMAT treats square roots of numbers? Thanks![/quot a=b+4 ===> ab=4 A is ok
(ab)^2=16 ====> ab= +4 and ab= 4 so we got two answer not ok
remember this AD OR BCE when B is not ok then D obviously is not ok
we go with A then between A and D



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Re: What is the value of a  b? (1) a = b + 4 (2) (a  b)^2 = 1
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16 Sep 2016, 15:07
ab = ?
(1) a = b+4 > ab =4
(2) (ab)^2 = 16 > ab = +/ (4)
(1) gives us a definitive answer where (2) is ambiguous > hence A is the correct answer



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Re: What is the value of a  b? (1) a = b + 4 (2) (a  b)^2 = 1
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09 Dec 2016, 06:59
Could someone please help me explain this very basic concept? or give an example of how b might be larger than a, and a larger than b
On the other hand, if the expression would be (a+b)^2 = 16 , would this only yield one possible answer, 4? thank you



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Re: What is the value of a  b? (1) a = b + 4 (2) (a  b)^2 = 1
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29 Jan 2018, 12:20
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