GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 24 Mar 2019, 06:13

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

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

Which of the following is equivalent to 21/6 ?

Author Message
TAGS:

Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 53798
Which of the following is equivalent to 21/6 ?  [#permalink]

Show Tags

06 Jun 2017, 10:01
1
8
00:00

Difficulty:

35% (medium)

Question Stats:

62% (01:17) correct 38% (01:28) wrong based on 233 sessions

HideShow timer Statistics

Which of the following is equivalent to $$\frac{\sqrt{21}}{6}$$?

A. $$\frac{\sqrt{7}}{2}$$

B. 7/12

C. $$\sqrt{\frac{7}{2}}$$

D. $$\sqrt{\frac{7}{12}}$$

E. $$\frac{7\sqrt{3}}{2}$$

_________________
Senior PS Moderator
Joined: 26 Feb 2016
Posts: 3362
Location: India
GPA: 3.12
Which of the following is equivalent to 21/6 ?  [#permalink]

Show Tags

06 Jun 2017, 10:25
1
1
$$\frac{\sqrt{21}}{6}$$ = $$\frac{\sqrt{7*3}}{6}$$

= $$\frac{\sqrt{7*3}}{\sqrt{36}}$$

= $$\frac{\sqrt{7*3}}{\sqrt{12*3}}$$ = $$\sqrt{\frac{7}{12}}$$ (Option D)
_________________

You've got what it takes, but it will take everything you've got

CEO
Joined: 12 Sep 2015
Posts: 3516
Re: Which of the following is equivalent to 21/6 ?  [#permalink]

Show Tags

06 Jun 2017, 11:08
Top Contributor
Bunuel wrote:
Which of the following is equivalent to $$\frac{\sqrt{21}}{6}$$?

A. $$\frac{\sqrt{7}}{2}$$

B. 7/12

C. $$\sqrt{\frac{7}{2}}$$

D. $$\sqrt{\frac{7}{12}}$$

E. $$\frac{7\sqrt{3}}{2}$$

Useful rule: $$\frac{\sqrt{x}}{\sqrt{y}} = {\sqrt{\frac{x}{y}}}$$

So, $$\frac{\sqrt{21}}{6} =\frac{\sqrt{21}}{\sqrt{36}} = {\sqrt{\frac{21}{36}}} = {\sqrt{\frac{7}{12}}}$$

_________________

Test confidently with gmatprepnow.com

Current Student
Joined: 06 Sep 2016
Posts: 131
Location: Italy
Schools: EDHEC (A$) GMAT 1: 650 Q43 V37 GPA: 3.2 WE: General Management (Human Resources) Re: Which of the following is equivalent to 21/6 ? [#permalink] Show Tags 27 Jun 2017, 02:41 Why in this case it's wrong to square all and remove the square root? In this question https://gmatclub.com/forum/2-240047.html I saw that it's feasible... why in this case it isn't? Senior PS Moderator Joined: 26 Feb 2016 Posts: 3362 Location: India GPA: 3.12 Which of the following is equivalent to 21/6 ? [#permalink] Show Tags 27 Jun 2017, 03:34 MvArrow wrote: Why in this case it's wrong to square all and remove the square root? In this question https://gmatclub.com/forum/2-240047.html I saw that it's feasible... why in this case it isn't? Let a= $$\frac{\sqrt{21}}{6}$$ If you want to remove the square root, square both sides $$a^2 =\frac{21}{6^2}$$ = $$\frac{21}{36} = \frac{7*3}{12*3} = \frac{7}{12}$$ Taking square root, we get a = $$\sqrt{\frac{7}{12}}$$(Option D) Hope it helps! _________________ You've got what it takes, but it will take everything you've got Math Expert Joined: 02 Sep 2009 Posts: 53798 Re: Which of the following is equivalent to 21/6 ? [#permalink] Show Tags 27 Jun 2017, 03:35 1 MvArrow wrote: Which of the following is equivalent to $$\frac{\sqrt{21}}{6}$$? A. $$\frac{\sqrt{7}}{2}$$ B. 7/12 C. $$\sqrt{\frac{7}{2}}$$ D. $$\sqrt{\frac{7}{12}}$$ E. $$\frac{7\sqrt{3}}{2}$$ Why in this case it's wrong to square all and remove the square root? In this question https://gmatclub.com/forum/2-240047.html I saw that it's feasible... why in this case it isn't? You can do this way but you should square the options too to compare apples with apples. When you square, the question becomes: which of the following is equivalent to $$(\frac{\sqrt{21}}{6})^2=\frac{21}{36}=\frac{7}{12}$$. Option D squared gives exactly this value: $$(\sqrt{\frac{7}{12}})^2=\frac{7}{12}$$ Answer: D. Hope it helps. _________________ Director Joined: 13 Mar 2017 Posts: 704 Location: India Concentration: General Management, Entrepreneurship GPA: 3.8 WE: Engineering (Energy and Utilities) Re: Which of the following is equivalent to 21/6 ? [#permalink] Show Tags 27 Jun 2017, 03:55 Bunuel wrote: Which of the following is equivalent to $$\frac{\sqrt{21}}{6}$$? A. $$\frac{\sqrt{7}}{2}$$ B. 7/12 C. $$\sqrt{\frac{7}{2}}$$ D. $$\sqrt{\frac{7}{12}}$$ E. $$\frac{7\sqrt{3}}{2}$$ $$\frac{\sqrt{21}}{6}$$ $$\frac{\sqrt{7*3}}{\sqrt{3*3*2*2}}$$ $$\frac{\sqrt{7}}{\sqrt{3*2*2}}$$ $$\frac{\sqrt{7}}{\sqrt{12}}$$ Answer D. _________________ CAT 2017 (98.95) & 2018 (98.91) : 99th percentiler UPSC Aspirants : Get my app UPSC Important News Reader from Play store. MBA Social Network : WebMaggu Appreciate by Clicking +1 Kudos ( Lets be more generous friends.) What I believe is : "Nothing is Impossible, Even Impossible says I'm Possible" : "Stay Hungry, Stay Foolish". Current Student Joined: 06 Sep 2016 Posts: 131 Location: Italy Schools: EDHEC (A$)
GMAT 1: 650 Q43 V37
GPA: 3.2
WE: General Management (Human Resources)
Re: Which of the following is equivalent to 21/6 ?  [#permalink]

Show Tags

27 Jun 2017, 04:16
Bunuel wrote:
MvArrow wrote:
Which of the following is equivalent to $$\frac{\sqrt{21}}{6}$$?

A. $$\frac{\sqrt{7}}{2}$$

B. 7/12

C. $$\sqrt{\frac{7}{2}}$$

D. $$\sqrt{\frac{7}{12}}$$

E. $$\frac{7\sqrt{3}}{2}$$

Why in this case it's wrong to square all and remove the square root?
In this question https://gmatclub.com/forum/2-240047.html I saw that it's feasible... why in this case it isn't?

You can do this way but you should square the options too to compare apples with apples. When you square, the question becomes: which of the following is equivalent to $$(\frac{\sqrt{21}}{6})^2=\frac{21}{36}=\frac{7}{12}$$. Option D squared gives exactly this value: $$(\sqrt{\frac{7}{12}})^2=\frac{7}{12}$$

Hope it helps.

Great! Thanks! I din't think about it
Non-Human User
Joined: 09 Sep 2013
Posts: 10190
Re: Which of the following is equivalent to 21/6 ?  [#permalink]

Show Tags

24 Feb 2019, 09:01
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.
_________________
Re: Which of the following is equivalent to 21/6 ?   [#permalink] 24 Feb 2019, 09:01
Display posts from previous: Sort by