OG 13 -120

This topic has expert replies
Master | Next Rank: 500 Posts
Posts: 429
Joined: Wed Sep 19, 2012 11:38 pm
Thanked: 6 times
Followed by:4 members

OG 13 -120

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



Your Answer






Global Stats

The other way to solve this
OG 120.rtf
Is there any other way to reach this answer?
(1.83 MiB) Downloaded 147 times

User avatar
Master | Next Rank: 500 Posts
Posts: 447
Joined: Sun Apr 22, 2012 7:13 am
Thanked: 46 times
Followed by:13 members
GMAT Score:700

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.

User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pm
Location: New York, NY
Thanked: 13060 times
Followed by:1906 members
GMAT Score:790

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.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3


User avatar
GMAT Instructor
Posts: 16207
Joined: Mon Dec 08, 2008 6:26 pm
Location: Vancouver, BC
Thanked: 5254 times
Followed by:1268 members
GMAT Score:770

by Brent@GMATPrepNow » 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
Brent Hanneson - Creator of GMATPrepNow.com

GMAT Instructor
Posts: 2630
Joined: Wed Sep 12, 2012 3:32 pm
Location: East Bay all the way
Thanked: 625 times
Followed by:119 members
GMAT Score:780

by Matt@VeritasPrep » 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


User avatar
Elite Legendary Member
Posts: 10392
Joined: Sun Jun 23, 2013 6:38 pm
Location: Palo Alto, CA
Thanked: 2867 times
Followed by:511 members
GMAT Score:800

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

GMAT Assassins aren’t born, they’re made,
Contact Rich at [email protected]