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Updated on: 21 Nov 2013, 02:21
Originally posted by registerincog on 21 Nov 2013, 02:10.
Last edited by Bunuel on 21 Nov 2013, 02:21, edited 2 times in total.
Last edited by Bunuel on 21 Nov 2013, 02:21, edited 2 times in total.
Edited the question.
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C
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
45%
(medium)
Question Stats:
70% (01:37) correct
30%
(01:57)
wrong
based on 1165
sessions
History
Date
Time
Result
Not Attempted Yet
The expression \((\sqrt{8 +\sqrt{63}} +\sqrt{8 -\sqrt{63}})^2\) =
A) 20
B) 19
C) 18
D) 17
E) 16
A) 20
B) 19
C) 18
D) 17
E) 16
registerincog
\((\sqrt{8 +\sqrt{63}} +\sqrt{8 -\sqrt{63}})^2= \)
\( =(8 +\sqrt{63})+2\sqrt{(8 +\sqrt{63})(8 -\sqrt{63})}+(8 -\sqrt{63})= \)
\( =16+2\sqrt{64-63}= \)
\( =18\).
Answer: C.
General Discussion
22 Dec 2014, 15:18
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Hi registerincog,
Since it's been over a year since you posted, I'm not sure if you're still around to see this, but this question is more about pattern-recognition than anything else.
Bunuel has already shown how the math works, so I won't rehash that here. Instead, I'll offer some perspective.
The GMAT Quant section is going to test you on a lot of standard math rules/ideas/formulas/etc., but will sometimes test you on these rules in ways that you're not used to thinking about. When you find yourself looking at a question that is based on some "crazy-looking" numbers, then chances are really good that the question is built around a pattern of some kind (and it's a pattern that you KNOW in some other simpler format).
Here, if you ignore the numbers and square root signs, you really just have this:
(X+Y)^2
This is one of 3 Classic Quadratics that you MUST have memorized for Test Day.
(X+Y)^2 = X^2 + 2XY + Y^2
Now you can plug back in the relative values for X and Y and simplify. The "math" won't be fun, but its based on standard arithmetic rules (using radicals, multiplication, combining like terms, etc.).
GMAT assassins aren't born, they're made,
Rich
Since it's been over a year since you posted, I'm not sure if you're still around to see this, but this question is more about pattern-recognition than anything else.
Bunuel has already shown how the math works, so I won't rehash that here. Instead, I'll offer some perspective.
The GMAT Quant section is going to test you on a lot of standard math rules/ideas/formulas/etc., but will sometimes test you on these rules in ways that you're not used to thinking about. When you find yourself looking at a question that is based on some "crazy-looking" numbers, then chances are really good that the question is built around a pattern of some kind (and it's a pattern that you KNOW in some other simpler format).
Here, if you ignore the numbers and square root signs, you really just have this:
(X+Y)^2
This is one of 3 Classic Quadratics that you MUST have memorized for Test Day.
(X+Y)^2 = X^2 + 2XY + Y^2
Now you can plug back in the relative values for X and Y and simplify. The "math" won't be fun, but its based on standard arithmetic rules (using radicals, multiplication, combining like terms, etc.).
GMAT assassins aren't born, they're made,
Rich
