Find all School-related info fast with the new School-Specific MBA Forum

It is currently 21 Oct 2014, 16:19

Close

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

If m and n are both positive, what is the value of m*root(n)

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
1 KUDOS received
Intern
Intern
avatar
Joined: 04 May 2009
Posts: 14
Followers: 0

Kudos [?]: 3 [1] , given: 0

If m and n are both positive, what is the value of m*root(n) [#permalink] New post 16 May 2009, 11:26
1
This post received
KUDOS
00:00
A
B
C
D
E

Difficulty:

  35% (medium)

Question Stats:

59% (02:01) correct 41% (01:06) wrong based on 137 sessions
If m and n are both positive, what is the value of m*\sqrt{n}?

(1) \frac{m*n}{\sqrt{n}}=10
(2) \frac{m^2*n}{2}=50

[Reveal] Spoiler:
I thought I was doing well understanding the difference between taking a square root and unsquaring a variable. Then I ran into the following DS problem:

If m and n are both positive, what is the value of m\sqrt{n} ?

1.\frac{m*n} {\sqrt{n}}= 10 (this is sufficient, no problem there)
2. m^2*n = 100

For statement 2, the explanation in the book says that we take the positive square root of both sides to obtain m√n = 10. If -10 is not a solution here, then (2) would indeed be suffcient.

But how is that different from saying we are unsquaring (m√n)^2, which would yield m√n = 10, -10 ?

As an example, the number properties guide in mgmt claims that x^2 = 4 has two solutions, x=2 and x=-2. That makes sense and I'm just not seeing what's different here.
[Reveal] Spoiler: OA
Director
Director
User avatar
Joined: 01 Apr 2008
Posts: 909
Schools: IIM Lucknow (IPMX) - Class of 2014
Followers: 15

Kudos [?]: 233 [0], given: 18

Re: DS Problem - "unsquaring" vs taking a square root [#permalink] New post 27 Sep 2009, 20:35
This is a specific concept about GMAT.

If you know that the sign of the variable inside the square root is positive then ALWAYS ignore the negative value.
Intern
Intern
avatar
Joined: 23 Sep 2009
Posts: 11
Location: uzbekistan
Schools: Chicago booth,Dartmouth,Duke
Followers: 0

Kudos [?]: 1 [0], given: 0

Re: DS Problem - "unsquaring" vs taking a square root [#permalink] New post 31 Dec 2009, 03:37
for this problem:

m^2*n=100
m^2=100\n
m=sqrt(100\n)

since no number is -ve when sqrt the answer is d
Manager
Manager
avatar
Joined: 29 Apr 2010
Posts: 79
Followers: 1

Kudos [?]: 11 [0], given: 1

Tricky DS question [#permalink] New post 29 Apr 2010, 23:57
If m and n are both positive, what is the value of m*\sqrt{n}?

(1) \frac{m*n}{\sqrt{n}}=10

(2) \frac{m^2*n}{2}=50

The textbook answer says (D) but the Square root of choice (2) will give us +/- 10.
Should we ignore -10 and conclude that (2) also gives us the answer

Last edited by Bunuel on 30 Apr 2010, 00:15, edited 3 times in total.
Formating
Expert Post
2 KUDOS received
Math Expert
User avatar
Joined: 02 Sep 2009
Posts: 23357
Followers: 3604

Kudos [?]: 28727 [2] , given: 2839

Re: Tricky DS question [#permalink] New post 30 Apr 2010, 00:34
2
This post received
KUDOS
Expert's post
Merged similar topics.

achan wrote:
If m and n are both positive, what is the value of m*\sqrt{n}?

(1) \frac{m*n}{\sqrt{n}}=10

(2) \frac{m^2*n}{2}=50

The textbook answer says (D) but the Square root of choice (2) will give us +/- 10.
Should we ignore -10 and conclude that (2) also gives us the answer


Theory:

GMAT is dealing only with Real Numbers: Integers, Fractions and Irrational Numbers.

When the GMAT provides the square root sign for an even root, such as \sqrt{x} or \sqrt[4]{x}, then the only accepted answer is the positive root.

That is, \sqrt{25}=5, NOT +5 or -5. In contrast, the equation x^2=25 has TWO solutions, +5 and -5. Even roots have only a positive value on the GMAT.

Odd roots will have the same sign as the base of the root. For example, \sqrt[3]{125} =5 and \sqrt[3]{-64} =-4.


Back to the original question:

If m and n are both positive, what is the value of m*\sqrt{n}?

(1) \frac{m*n}{\sqrt{n}}=10 --> reduce by \sqrt{n} --> m*\sqrt{n}=10. Sufficient.

(2) \frac{m^2*n}{2}=50 --> (m*\sqrt{n})^2=100 --> m*\sqrt{n}=10 or m*\sqrt{n}=-10. BUT since m and n are both positive (given) m*\sqrt{n} can not equal to -10. Hence only one solution is valid: m*\sqrt{n}=10. Sufficient.

Answer: D.

Hope it helps.
_________________

NEW TO MATH FORUM? PLEASE READ THIS: ALL YOU NEED FOR QUANT!!!

PLEASE READ AND FOLLOW: 11 Rules for Posting!!!

RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory; 7. Remainders; 8. Overlapping Sets; 9. PDF of Math Book; 10. Remainders; 11. GMAT Prep Software Analysis NEW!!!; 12. SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) NEW!!!; 12. Tricky questions from previous years. NEW!!!;

COLLECTION OF QUESTIONS:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS ; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
25 extra-hard Quant Tests

Get the best GMAT Prep Resources with GMAT Club Premium Membership

CEO
CEO
User avatar
Joined: 09 Sep 2013
Posts: 2823
Followers: 206

Kudos [?]: 42 [0], given: 0

Premium Member
Re: If m and n are both positive, what is the value of m*root(n) [#permalink] New post 24 Dec 2013, 14:44
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________

GMAT Books | GMAT Club Tests | Best Prices on GMAT Courses | GMAT Mobile App | Math Resources | Verbal Resources

Re: If m and n are both positive, what is the value of m*root(n)   [#permalink] 24 Dec 2013, 14:44
    Similar topics Author Replies Last post
Similar
Topics:
1 if m and n are both positives, what is the value of Dreaming 14 24 Sep 2011, 04:31
What is the value of positive integer n? Madelaine88 6 28 Feb 2011, 01:31
If m and n are both positive integers and m>n is 6 a tejal777 2 18 Jul 2009, 00:32
1 m and n are positive integers. If m/n and m+n both are even, nirimblf 15 05 Jul 2008, 23:32
If M and N are both positive, what is the value of M sqrt N? remgeo 5 28 Nov 2005, 04:44
Display posts from previous: Sort by

If m and n are both positive, what is the value of m*root(n)

  Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| Privacy Policy| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group and phpBB SEO

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.