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If y = 5 + x and y = 12  x, and if y^2 = x^2 + k, then k equals which
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Updated on: 03 Jul 2017, 08:55
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If y = 5 + x and y = 12  x, and if y^2 = x^2 + k, then k equals which of the following? A. 17 B. 25 C. 50 D. 60 E. 100
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Originally posted by mkrishnabdrr on 02 Jul 2017, 21:36.
Last edited by bb on 03 Jul 2017, 08:55, edited 3 times in total.
Renamed the topic and edited the question.




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Re: If y = 5 + x and y = 12  x, and if y^2 = x^2 + k, then k equals which
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02 Jul 2017, 22:06
Given data : yx = 5 y+x = 12 Since \(y^2\)=\(x^2\)+k k = \(y^2\)  \(x^2\) k = (y+x)(yx) = 5*12 = 60(Option D)
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Re: If y = 5 + x and y = 12  x, and if y^2 = x^2 + k, then k equals which
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03 Jul 2017, 08:29
mkrishnabdrr wrote: If y = 5 + x and y = 12  x, and if y^2 = x^2 + k, then k equals which of the following?
A. 17 B. 25 C. 50 D. 60 E. 100 \(12  x = 5 + x\) Or, \(7 = 2x\) Or, \(x = \frac{7}{2}\) So, \(y = 5 + \frac{7}{2}\) Or, \(y = \frac{17}{2}\) Given  \(y^2 = x^2 + k\) \(\frac{17*17}{2*2} = \frac{7*7}{2*2} + k\) Or, \(\frac{289}{4} = \frac{49}{4} + k\) Or, \(k = \frac{240}{4}\) So, \(k = 60\) , answer must be (D)
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Re: If y = 5 + x and y = 12  x, and if y^2 = x^2 + k, then k equals which
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03 Jul 2017, 17:46
Abhishek009 wrote: mkrishnabdrr wrote: If y = 5 + x and y = 12  x, and if y^2 = x^2 + k, then k equals which of the following?
A. 17 B. 25 C. 50 D. 60 E. 100 \(12  x = 5 + x\) Or, \(7 = 2x\) Or, \(x = \frac{7}{2}\) So, \(y = 5 + \frac{7}{2}\) Or, \(y = \frac{17}{2}\) Given  \(y^2 = x^2 + k\) \(\frac{17*17}{2*2} = \frac{7*7}{2*2} + k\) Or, \(\frac{289}{4} = \frac{49}{4} + k\) Or, \(k = \frac{240}{4}\) So, \(k = 60\) , answer must be (D)The trick to solving this question is recognizing that \(y^2\)\(x^2\)=(y+x)(yx) y = 5 + x or, yx=5 y = 12  x or, y+x=12 \(y^2\) = \(x^2\)+ k or, \(y^2\)\(x^2\)=k or, (y+x)(yx)=k or, 12 * 5 =k i.e. k = 60 Hence, Ans is D
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How to recognize "triggers"
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16 Apr 2018, 09:45
Hi everyone, New here. Story in brief is that I'm looking for a change in career. Anyway  I've been using Magoosh GMAT prep and for the life of me my quant skills are teh suck. My career path took me as far away from math as possible (yes I know the GRE is less math intensive but I figured I'd use the harder prep to cover more stuff)  Anyway  Here's a practice problem from Magoosh: If y = x + 5 and y = 12  x and \(y^2 = x^2 + K\) then K equals which of the following: Choices given (A) 17, (B) 25, (C) 60, (D) 119. How is one supposed to recognize where to even begin? In the interest of getting as many approaches as possible, I won't go into what Magoosh says to do. Help appreciated  ice



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How to recognize "triggers"
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16 Apr 2018, 13:59
icedoverfire wrote: Hi everyone, New here. Story in brief is that I'm looking for a change in career. Anyway  I've been using Magoosh GMAT prep and for the life of me my quant skills are teh suck. My career path took me as far away from math as possible (yes I know the GRE is less math intensive but I figured I'd use the harder prep to cover more stuff)  Anyway  Here's a practice problem from Magoosh: If y = x + 5 and y = 12  x and \(y^2 = x^2 + K\) then K equals which of the following: Choices given (A) 17, (B) 25, (C) 60, (D) 119. How is one supposed to recognize where to even begin? In the interest of getting as many approaches as possible, I won't go into what Magoosh says to do. Help appreciated  ice At first, you can start combining the first 2 equations. 12x=x+5 2x=7 x=3.5 y=8.5 y^2 = x^2 +k or y^2  x^2 = k now, this will be burdensome to calculate with decimals. on another side, we can calculate (yx)(y+x), which is basically y^2  x^2. now yx and y+x is easier to calculate, and their product is easier to calculate as well. yx = 5 y+x = 12 5*12 = 60. K is 60. It takes time to form the number sense and start seeing the way you would approach this question. the approach may vary, depending on how easy it is for you.



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Re: How to recognize "triggers"
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16 Apr 2018, 14:06
icedoverfire wrote: Hi everyone, New here. Story in brief is that I'm looking for a change in career. Anyway  I've been using Magoosh GMAT prep and for the life of me my quant skills are teh suck. My career path took me as far away from math as possible (yes I know the GRE is less math intensive but I figured I'd use the harder prep to cover more stuff)  Anyway  Here's a practice problem from Magoosh: If y = x + 5 and y = 12  x and \(y^2 = x^2 + K\) then K equals which of the following: Choices given (A) 17, (B) 25, (C) 60, (D) 119. How is one supposed to recognize where to even begin? In the interest of getting as many approaches as possible, I won't go into what Magoosh says to do. Help appreciated  ice y = (x + 5) and y = (12  x) => (x + 5) = (12  x) => x =3.5, hense y=12x=123.5=8.5 \(y^2 = x^2 + K\) => \(K=y^2  x^2\) = (yx)(y+x) =(8.53.5)(8.5+3.5)=5*12=60. Answer (C)



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Re: If y = 5 + x and y = 12  x, and if y^2 = x^2 + k, then k equals which
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16 Apr 2018, 23:22
icedoverfire wrote: Hi everyone, New here. Story in brief is that I'm looking for a change in career. Anyway  I've been using Magoosh GMAT prep and for the life of me my quant skills are teh suck. My career path took me as far away from math as possible (yes I know the GRE is less math intensive but I figured I'd use the harder prep to cover more stuff)  Anyway  Here's a practice problem from Magoosh: If y = x + 5 and y = 12  x and \(y^2 = x^2 + K\) then K equals which of the following: Choices given (A) 17, (B) 25, (C) 60, (D) 119. How is one supposed to recognize where to even begin? In the interest of getting as many approaches as possible, I won't go into what Magoosh says to do. Help appreciated  ice Merging topics. Please refer to the discussion above. From my point of view, the best approach is given by pushpitkc HERE.
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Re: If y = 5 + x and y = 12  x, and if y^2 = x^2 + k, then k equals which
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18 Apr 2018, 10:37
Given : y= 5+x and y=12x then 5+x=12x =>x=7/2 And y^2=x^2+k=> (5+2)^2=x^2+k =>x^2+10x+25=x^2+k =>10(7/2)+25=k k=60(Ans C)




Re: If y = 5 + x and y = 12  x, and if y^2 = x^2 + k, then k equals which &nbs
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18 Apr 2018, 10:37






