Last visit was: 11 Sep 2026, 13:32 It is currently 11 Sep 2026, 13:32
Home
Messages
Tests
Schools
Events
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.
Go to My Error Log Learn more
Close
Request Expert Reply
Confirm Cancel
User avatar
catgmat
User avatar
Joined: 27 Mar 2007
Last visit: 10 Jan 2011
Posts: 187
Own Kudos:
159
Posts: 187
Kudos: 159
PowerPrep: Radicals Updated on: 24 Jun 2007, 12:04
Originally posted by catgmat on 23 Jun 2007, 00:27.
Last edited by catgmat on 24 Jun 2007, 12:04, edited 2 times in total.
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Please explain, OA is E! Cheers



Archived Topic
Hi there,
This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
Where to now? Join ongoing discussions on thousands of quality questions in our Quantitative Questions Forum
Still interested in this question? Check out the "Best Topics" block below for a better discussion on this exact question, as well as several more related questions.
Thank you for understanding, and happy exploring!
User avatar
catgmat
User avatar
Joined: 27 Mar 2007
Last visit: 10 Jan 2011
Posts: 187
Own Kudos:
159
Posts: 187
Kudos: 159
PowerPrep: Radicals 24 Jun 2007, 02:45
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Could someone try to explain, please? cheers
User avatar
AugiTh
User avatar
Joined: 23 Apr 2007
Last visit: 18 Aug 2010
Posts: 86
Own Kudos:
500
Posts: 86
Kudos: 500
PowerPrep: Radicals 24 Jun 2007, 11:16
Kudos
Add Kudos
Bookmarks
Bookmark this Post
put 9 as sqrt(81) and then use (a+b)^2 = a^2 + b^2 + 2ab formula

you get
sqrt(81) + sqrt(80) +sqrt(81) -sqrt(80) + 2*sqrt(sqrt(81)+sqrt(80))*(sqrt(sqrt(81)-sqrt(80)) -> eq1

sqrt(sqrt(81)+sqrt(80))*(sqrt(sqrt(81)-sqrt(80)) is in
(a+b)*(a-b)=a^2-^b^2
Therefore sqrt(sqrt(81)+sqrt(80))*(sqrt(sqrt(81)-sqrt(80))
= sqrt(81-80) =1

thus eq1 becomes

sqrt(81) +sqrt(81) + 2

which gives 9+9+2 =20

hope this helps
User avatar
catgmat
User avatar
Joined: 27 Mar 2007
Last visit: 10 Jan 2011
Posts: 187
Own Kudos:
159
Posts: 187
Kudos: 159
PowerPrep: Radicals 24 Jun 2007, 13:18
Kudos
Add Kudos
Bookmarks
Bookmark this Post
AugiTh
put 9 as sqrt(81) and then use (a+b)^2 = a^2 + b^2 + 2ab formula

you get
sqrt(81) + sqrt(80) +sqrt(81) -sqrt(80) + 2*sqrt(sqrt(81)+sqrt(80))*(sqrt(sqrt(81)-sqrt(80)) -> eq1

sqrt(sqrt(81)+sqrt(80))*(sqrt(sqrt(81)-sqrt(80)) is in
(a+b)*(a-b)=a^2-^b^2
Therefore sqrt(sqrt(81)+sqrt(80))*(sqrt(sqrt(81)-sqrt(80))
= sqrt(81-80) =1

thus eq1 becomes

sqrt(81) +sqrt(81) + 2

which gives 9+9+2 =20

hope this helps
Show more


thanks a lot mate! now I got it. cheers
User avatar
ian7777
User avatar
Joined: 09 Mar 2003
Last visit: 24 Jan 2010
Posts: 227
Own Kudos:
178
Posts: 227
Kudos: 178
PowerPrep: Radicals 24 Jun 2007, 14:37
Kudos
Add Kudos
Bookmarks
Bookmark this Post
this is kind of crazy, but i did it differently.

WIthout making 9 root 81, i squared the same way, and we end up with

18 + 2*Root(9+root80)*root(9-root80)

Wasn't sure what to do with the second part there, so I just squared the whole thing, that way I'd get rid of the outter radicals, figuring I could square root it again when I was done.

Turns out, I was right, because when you do that, you just get 4. Then I square rooted it again back to 2, and then you've just got

18+2

20



Archived Topic
Hi there,
This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
Where to now? Join ongoing discussions on thousands of quality questions in our Quantitative Questions Forum
Still interested in this question? Check out the "Best Topics" block above for a better discussion on this exact question, as well as several more related questions.
Thank you for understanding, and happy exploring!