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Updated on: 17 Oct 2018, 05:04
Originally posted by mikemcgarry on 13 Mar 2013, 11:11.
Last edited by Bunuel on 17 Oct 2018, 05:04, edited 1 time in total.
Last edited by Bunuel on 17 Oct 2018, 05:04, edited 1 time in total.
Renamed the topic and edited the question.
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A
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
15%
(low)
Question Stats:
82% (01:33) correct
18%
(02:13)
wrong
based on 672
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Not Attempted Yet
\(x*(5 + \sqrt 7) = 90\). In the equation above, x =
(A) \(5*(5 - \sqrt 7)\)
(B) \(\frac{15}{2}\)
(C) \(15\)
(D) \(90*(5 - \sqrt 7)\)
(E) \(90*(5 + \sqrt 7)\)
For a full discussion of how to divide by radicals and radical expressions, as well as a complete solution to this particular problem, see this blog:
https://magoosh.com/gmat/2013/gmat-math- ... uare-root/
Mike
(A) \(5*(5 - \sqrt 7)\)
(B) \(\frac{15}{2}\)
(C) \(15\)
(D) \(90*(5 - \sqrt 7)\)
(E) \(90*(5 + \sqrt 7)\)
For a full discussion of how to divide by radicals and radical expressions, as well as a complete solution to this particular problem, see this blog:
https://magoosh.com/gmat/2013/gmat-math- ... uare-root/
Mike
15 Mar 2013, 11:54
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\(x*(5+\sqrt{7})=90\)
Just rationalize \(x=\frac{90}{(5+\sqrt{7})}\)
by multiplying and dividing by \((5-\sqrt{7})\)
- The numerator will be: \(90*(5-\sqrt{7})\)
- And the denominator will be: \(25-5*\sqrt{7}+5*\sqrt{7}-7=25-7=18\)
The solution is \(5*(5-\sqrt{7})\)
Solution A
Just rationalize \(x=\frac{90}{(5+\sqrt{7})}\)
by multiplying and dividing by \((5-\sqrt{7})\)
- The numerator will be: \(90*(5-\sqrt{7})\)
- And the denominator will be: \(25-5*\sqrt{7}+5*\sqrt{7}-7=25-7=18\)
The solution is \(5*(5-\sqrt{7})\)
Solution A
General Discussion
13 Mar 2013, 13:08
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It's A.
\(5*(5-\sqrt{7})(5+\sqrt{7})=\)
\(5*(5^2+\sqrt{7}^2)=\)
\(5*18=\)
\(90\)
\(5*(5-\sqrt{7})(5+\sqrt{7})=\)
\(5*(5^2+\sqrt{7}^2)=\)
\(5*18=\)
\(90\)
