OG 13 -120

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OG 13 -120

by [email protected] » Wed Apr 03, 2013 2:22 am



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The other way to solve this
OG 120.rtf
Is there any other way to reach this answer?
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by hemant_rajput » Wed Apr 03, 2013 4:19 am
[email protected] wrote:The other way to solve this
Why you need another way? The way mentioned in the explanation is the easiest and quickest way to solve the given question. Solution doesn't even involve any calculation.
I'm no expert, just trying to work on my skills. If I've made any mistakes please bear with me.

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by GMATGuruNY » Wed Apr 03, 2013 8:42 am
If s>0 and √(r/s) = s, what is r in terms of s?

A) 1/s
B) √s
C) s√s
D) s³
E) s² - s
I would recommend straight algebra:

( √(r/s) )² = s²
r/s = s²
r = s³.

The correct answer is D.

An alternate approach is to plug in an easy value for s and solve for r.

If s=2, we get:
√(r/2) = 2.

Since √4 = 2, the value under the square root -- r/2 -- must be equal to 4:
r/2 = 4.
r = 8. This is our target.

Now we plug s=2 into the answer choices to see which yields our target of 8.
Only D works:
s³ = 2³ = 8.

For this problem, algebra seems easier and more efficient.
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by [email protected] » Wed Aug 30, 2017 1:31 pm
If s > 0 and √(r/s) = s, what is r in terms of s ?

(A) 1/s
(B) √s
(C) s√s
(D) s^3
(E) s^2 - s
Let's test some values that satisfy the given equation √(r/s) = s

For example, r = 125 and s = 5 satisfies the equation √(r/s) = s

What is r in terms of s ?
Check the answer choices to see which one yields 125 when s = 5

(A) 1/5 ≠ 125 ELIMINATE
(B) √5 ≠ 125 ELIMINATE
(C) 5√5 ≠ 125 ELIMINATE
(D) 5^3 = 125 KEEP!!
(E) 5^2 - 5 ≠ 125 ELIMINATE

Answer: D
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by [email protected] » Wed Aug 30, 2017 5:10 pm
Brent, resurrecting threads! A GMAT expert and a necromancer ... :D

Another way to do this one:

√(r/s) = s

square both sides:

r/s = s * s

multiply both sides by s:

r = s * s * s


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Re: OG 13 -120

by [email protected] » Sat Apr 24, 2021 7:48 pm
Hi All,

We’re told that S > 0 and root(R/S) = S. We’re asked for the value of R in terms of S.

Typically, when the phrase “in terms of” appears in a question, an Algebraic approach is required. However, this question can be solved rather easily by TESTing VALUES.

IF… S = 2, then root(R/S) = 2… meaning that R/2 has to equal 4. This means that R = 8… so we’re looking for an answer that equals 8 when S = 2. The answers are simple enough that you should be able to find the correct answer in a matter of seconds…

Final Answer: D

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