January 21, 2019 January 21, 2019 10:00 PM PST 11:00 PM PST Mark your calendars  All GMAT Club Tests are free and open January 21st for celebrate Martin Luther King Jr.'s Birthday. January 22, 2019 January 22, 2019 10:00 PM PST 11:00 PM PST In case you didn’t notice, we recently held the 1st ever GMAT game show and it was awesome! See who won a full GMAT course, and register to the next one.
Author 
Message 
TAGS:

Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 52343

Question Stats:
45% (01:19) correct 55% (01:10) wrong based on 205 sessions
HideShow timer Statistics



Math Expert
Joined: 02 Sep 2009
Posts: 52343

Re M0602
[#permalink]
Show Tags
15 Sep 2014, 23:26



Intern
Joined: 30 Jun 2012
Posts: 13

Re: M0602
[#permalink]
Show Tags
25 Nov 2014, 20:15
Why do we use absolute signs in this problem??



Math Expert
Joined: 02 Sep 2009
Posts: 52343

Re: M0602
[#permalink]
Show Tags
26 Nov 2014, 04:27



Intern
Joined: 25 May 2014
Posts: 46

Re: M0602
[#permalink]
Show Tags
05 Jan 2015, 01:18
Hi Bunuel, Agreed that as per the theory & property its \(\sqrt{x^2}=x\) But why can't we cancel out the square root with the power square? Because i did it as \(\sqrt{(x+3)^2}  \sqrt{(y1)^2}\) after cancelling the roots > (x+3)(y1)> \(xy+4 = 3/4  2/5 + 4\) and answer came out to be 87/20. Please help
_________________
Never Try Quitting, Never Quit Trying



Math Expert
Joined: 02 Sep 2009
Posts: 52343

Re: M0602
[#permalink]
Show Tags
05 Jan 2015, 04:53



Intern
Joined: 25 May 2014
Posts: 46

Re: M0602
[#permalink]
Show Tags
05 Jan 2015, 05:02
Bunuel wrote: Ankur9 wrote: Hi Bunuel, Agreed that as per the theory & property its \(\sqrt{x^2}=x\) But why can't we cancel out the square root with the power square? Because i did it as \(\sqrt{(x+3)^2}  \sqrt{(y1)^2}\) after cancelling the roots > (x+3)(y1)> \(xy+4 = 3/4  2/5 + 4\) and answer came out to be 87/20. Please help Because \(\sqrt{(x+3)^2}=x+3\), not x+3 and \(\sqrt{(y1)^2} = y1\), not y1. Check for more here: absolutevaluetipsandhints175002.html I checked the absolute tips and \(\sqrt{x^2}=x\) is given as one of the properties But how the property is derived or holds is not mentioned. Is this property holds because in GMAT only positive values are considered for even roots and thus \(\sqrt{x^2}=x\) right??
_________________
Never Try Quitting, Never Quit Trying



Math Expert
Joined: 02 Sep 2009
Posts: 52343

Re: M0602
[#permalink]
Show Tags
05 Jan 2015, 05:05
Ankur9 wrote: Bunuel wrote: Ankur9 wrote: Hi Bunuel, Agreed that as per the theory & property its \(\sqrt{x^2}=x\) But why can't we cancel out the square root with the power square? Because i did it as \(\sqrt{(x+3)^2}  \sqrt{(y1)^2}\) after cancelling the roots > (x+3)(y1)> \(xy+4 = 3/4  2/5 + 4\) and answer came out to be 87/20. Please help Because \(\sqrt{(x+3)^2}=x+3\), not x+3 and \(\sqrt{(y1)^2} = y1\), not y1. Check for more here: absolutevaluetipsandhints175002.html I checked the absolute tips and \(\sqrt{x^2}=x\) is given as one of the properties But how the property is derived or holds is not mentioned. Is this property holds because in GMAT only positive values are considered for even roots and thus \(\sqrt{x^2}=x\) right?? About \(\sqrt{x^2}=x\): The point here is that as square root function can not give negative result then \(\sqrt{some \ expression}\geq{0}\). So \(\sqrt{x^2}\geq{0}\). But what does \(\sqrt{x^2}\) equal to? Let's consider following examples: If \(x=5\) > \(\sqrt{x^2}=\sqrt{25}=5=x=positive\); If \(x=5\) > \(\sqrt{x^2}=\sqrt{25}=5=x=positive\). So we got that: \(\sqrt{x^2}=x\), if \(x\geq{0}\); \(\sqrt{x^2}=x\), if \(x<0\). What function does exactly the same thing? The absolute value function: \(x=x\), if \(x\geq{0}\) and \(x=x\), if \(x<0\). That is why \(\sqrt{x^2}=x\).
_________________
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: 24 Mar 2013
Posts: 24

Re: M0602
[#permalink]
Show Tags
14 Oct 2015, 10:33
Hi Bunuel, I understand your explanation. I wanted to apply the mod and solve this problem, However, we also know that..."When the GMAT provides the square root sign for an even root, then the only accepted answer is the positive root". So, the solution to this problem can go either way 87/20 (considering the positive roots only) or 63/20 ( with the mod approach) ...



Board of Directors
Joined: 17 Jul 2014
Posts: 2598
Location: United States (IL)
Concentration: Finance, Economics
GPA: 3.92
WE: General Management (Transportation)

Re: M0602
[#permalink]
Show Tags
14 Oct 2015, 10:55
rohitd80 wrote: Hi Bunuel, I understand your explanation. I wanted to apply the mod and solve this problem, However, we also know that..."When the GMAT provides the square root sign for an even root, then the only accepted answer is the positive root". So, the solution to this problem can go either way 87/20 (considering the positive roots only) or 63/20 ( with the mod approach) ... PEMDAS parentheses comes first. we cannot jump operations and square/take the square root of everything before solving for what is in parenthesis. y1 results in a negative expression. After squaring it, it gives us a positive expression. Moreover, after squaring everything, the square root will be as well a positive number. I did not do the way bunuel explained, yet I got to the right answer. sqrt[(x+3)^2] = sqrt[(3/4+12/4)^2] = sqrt[(15/4)^2]. this will result in 15/4. now let's take y sqrt[(y1)^2] = sqrt[(2/55/5)^2] = sqrt[(3/5)^2]. now, if we square 3/5 we get 9/25 which is a positive number. sqrt of 9/25 is 3/5. we got 15/4  3/5 multiply first by 5/5 and second by 4/4, the result is: (15*5)/20  (3*4)/20. extend this and get: (7512)/20. the result is 63/20.



Intern
Joined: 22 Mar 2015
Posts: 31

Re: M0602
[#permalink]
Show Tags
14 Dec 2015, 13:39
Hello Bunuel, As per Official Guide, x is defined to be x if x >= 0 and x if x < 0. Here it is x+3  y1 = 15/4  3/5. Now (y1) = 3/5 which is less than 0.
So shouldn't it be 15/4  3/5 = (15/4)  (3/5) = (15/4) + (3/5) = 87/20 ?
Kindly correct me if I'm making a mistake. Thanks.



Math Expert
Joined: 02 Sep 2009
Posts: 52343

Re: M0602
[#permalink]
Show Tags
17 Dec 2015, 08:19



Intern
Joined: 20 Mar 2016
Posts: 30

Re: M0602
[#permalink]
Show Tags
28 Jul 2016, 09:43
When the GMAT provides the square root sign for an even root, then the only accepted answer is the positive root . Thats why i didn't use mod. What am i missing here?



Math Expert
Joined: 02 Sep 2009
Posts: 52343

Re: M0602
[#permalink]
Show Tags
29 Jul 2016, 03:13



Manager
Joined: 03 Dec 2013
Posts: 70
Location: United States (HI)
GPA: 3.56

Re: M0602
[#permalink]
Show Tags
22 Aug 2016, 10:19
I think this is a highquality question and I agree with explanation. I think you can make this question a bit harder if you add 83/20 as an answer choice for people like me who forgot to take the absolute value into the consideration.



Intern
Joined: 17 Dec 2016
Posts: 13
Location: United States (NY)
Concentration: Sustainability
GPA: 3.76
WE: Other (Military & Defense)

Re: M0602
[#permalink]
Show Tags
25 Jul 2017, 18:46
I think this is a poorquality question and the explanation isn't clear enough, please elaborate.



Math Expert
Joined: 02 Sep 2009
Posts: 52343

Re: M0602
[#permalink]
Show Tags
25 Jul 2017, 19:16



Manager
Joined: 17 May 2017
Posts: 130
GPA: 3

Re: M0602
[#permalink]
Show Tags
26 Oct 2017, 00:55
I think this is a highquality question and I agree with explanation.



Intern
Status: Working my way to the MBA
Joined: 19 Nov 2017
Posts: 1
Location: Brazil
WE: Consulting (Consulting)

Re: M0602
[#permalink]
Show Tags
11 Feb 2018, 13:06
I think this is a highquality question and I agree with explanation. Explanation is fine. It's only missing a "+" sign between 3 and 3/4



Math Expert
Joined: 02 Sep 2009
Posts: 52343

Re: M0602
[#permalink]
Show Tags
11 Feb 2018, 20:45







Go to page
1 2
Next
[ 22 posts ]



