Problem Solving for 780+ Aspirants.

[This topic has 6 expert replies and 200 member replies]
Free $100 Amazon.com Gift Card - Buy a GMAT course using a Beat The GMAT discount code between Mar 8-22 and get a $100 Amazon.com Gift Card. Learn more!
Post New Topic   Post Reply

rohan_vus
Really wants to Beat The GMAT!

Default Avatar

Joined: 03 Apr 2008
Posts: 181

Thanks given: 1
Thanked 19 times in 18 posts
Location: USA

PostThu Sep 10, 2009 7:00 am

IMO B .

Let out of 100 x be no of students playing Rugby or Football or both . From question stem ratio of (Either Rugby or Football or both/None playing either) = 1/3 . So Number of students out of 100 playing neither of any sport is 3x ==> we have sone simple eqn , x + 3x = 100 , gives x = 25 .

Now x = nof only Rugby + nof Football only + nof football and rugby
so number of Football = 25 - 10 = 15
Back to top
View user's profile Send private message
bharathh
Really wants to Beat The GMAT!

Default Avatar

Joined: 27 Aug 2009
Posts: 159

Thanks given: 3
Thanked 14 times in 13 posts

PostThu Sep 10, 2009 8:09 am

Can you assume though that the students have to either play either sport or both sports or not play any sports at all?

Seems a bit vague to me. Unless that is the case I'd go with cannot calculate.
Back to top
View user's profile Send private message
rohan_vus
Really wants to Beat The GMAT!

Default Avatar

Joined: 03 Apr 2008
Posts: 181

Thanks given: 1
Thanked 19 times in 18 posts
Location: USA

PostThu Sep 10, 2009 8:16 am

Hi Bharath yes you are right ! i am assuming that there exist only 2 sports football and rubgy . I may be wrong . I feel question should have mentioned that only 2 sports exist .
Back to top
View user's profile Send private message
prindaroy
Really wants to Beat The GMAT!

Default Avatar

Joined: 16 Jul 2009
Posts: 113

Thanks given: 0
Thanked 13 times in 10 posts

Target GMAT Score: 790

PostSun Sep 13, 2009 3:44 pm

yes the question is a little vague. So, essentially, for out of every 7, three play football as well? Are these the only people playing football? so if there are 70 rugby players then 30 of them play football as well and 40 play only rugby? And so, if 10% of the people play only rugby, then the people playing football should be less right?
Back to top
View user's profile Send private message
duongthang
GMAT Destroyer!

Default Avatar

Joined: 20 May 2008
Posts: 739

Thanks given: 2
Thanked 6 times in 6 posts

PostMon Sep 21, 2009 6:33 am

angel ABO= angle ACO because they oposite the same arch in a circle

no need to prove. this concept is out of scope of GMAT.
Back to top
View user's profile Send private message
Talkativetree
Rising GMAT Star

Default Avatar

Joined: 13 Oct 2009
Posts: 41

Thanks given: 1
Thanked 0 times in 0 posts

PostMon Oct 19, 2009 9:33 pm

I love these hard problems. Oddly enough I think they're fun. Is there anywhere else I could find similar problems?
Back to top
View user's profile Send private message
Reply from GMAT/MBA Admissions Expert
Brent Hanneson
GMAT Instructor



Joined: 08 Dec 2008
Posts: 644

Thanks given: 9
Thanked 129 times in 113 posts
Location: Halfmoon Bay, BC

GMAT Score: 770

PostSat Oct 24, 2009 10:20 am

Talkativetree wrote:
I love these hard problems. Oddly enough I think they're fun. Is there anywhere else I could find similar problems?
You might try Magoosh.
Of the 500 questions there, I'd say that about 100-150 of them are in the 650+ range. (some of them have already been posted in the other forums)

_________________
Brent Hanneson, BSc, BEd, MEd
Online GMAT tutor
Founder - Leap Education
www.LeapEducation.ca
Content provider for www.Magoosh.com (GMAT practice questions with video solutions)

Be bold and mighty forces will come to your aid (Basil King)
Back to top
View user's profile Send private message
yregister
Just gettin' started!

Default Avatar

Joined: 28 Oct 2009
Posts: 5

Thanks given: 4
Thanked 0 times in 0 posts

PostTue Nov 03, 2009 7:33 pm

www.magoosh.com is awesome !! Thanks a lot Smile

Currently google's been saying its not a safe site. Well I ignored the message and nothing much happened. Just make sure you don't give ur credit card details anywhere in it Smile
Back to top
View user's profile Send private message
Reply from GMAT/MBA Admissions Expert
lunarpower
GMAT Instructor

Joined: 03 Mar 2008
Posts: 1213

Thanks given: 0
Thanked 221 times in 192 posts

GMAT Score: 800

PostSat Dec 19, 2009 10:46 pm

hey all.

regarding the "right triangle ABC" problem
(found here: http://www.beatthegmat.com/problem-solving-for-780-aspirants-t30325.html)

the solutions above would be nice in a geometry course; a lot of them are very pretty.

but - let's assume that this is a gmat problem. (NOTE: this would not conceivably be a gmat problem - it's too obscure/difficult to show up on the test.

if this were a gmat problem:
* it would be multiple choice, with five NUMBERS as answers - say, 30, 35, 40, 45, 50.
therefore:
* that NUMBER would be the same, regardless of the particular shape of the right triangle ABC.
therefore:
* if you can answer the problem for ANY SINGLE EXAMPLE of ABC, then you've got THE answer.


so:

we can just let ABC be a 45-45-90 triangle.
if that's the case, then BO will be a horizontal line, and it will be clear (from symmetry) that BO cuts right angle ABC into two 45-degree angles.
that's all you need.

again, BECAUSE THE PROBLEM WOULD BE MULTIPLE-CHOICE, there's no need to produce such elaborate general solutions; finding just one solution is sufficient.

_________________
ron purewal

instructor, mgmat

Learn more about me
Back to top
View user's profile Send private message
Reply from GMAT/MBA Admissions Expert
Ian Stewart
GMAT Instructor



Joined: 02 Jun 2008
Posts: 1581

Thanks given: 4
Thanked 425 times in 347 posts
Location: Toronto

GMAT Score: 780

PostSun Dec 20, 2009 10:44 am

lunarpower wrote:
hey all.

regarding the "right triangle ABC" problem
(found here: http://www.beatthegmat.com/problem-solving-for-780-aspirants-t30325.html)

the solutions above would be nice in a geometry course; a lot of them are very pretty.

but - let's assume that this is a gmat problem. (NOTE: this would not conceivably be a gmat problem - it's too obscure/difficult to show up on the test.

if this were a gmat problem:
* it would be multiple choice, with five NUMBERS as answers - say, 30, 35, 40, 45, 50.
therefore:
* that NUMBER would be the same, regardless of the particular shape of the right triangle ABC.
therefore:
* if you can answer the problem for ANY SINGLE EXAMPLE of ABC, then you've got THE answer.


so:

we can just let ABC be a 45-45-90 triangle.
if that's the case, then BO will be a horizontal line, and it will be clear (from symmetry) that BO cuts right angle ABC into two 45-degree angles.
that's all you need.

again, BECAUSE THE PROBLEM WOULD BE MULTIPLE-CHOICE, there's no need to produce such elaborate general solutions; finding just one solution is sufficient.
Great point, Ron - if you understand this, you can find simple solutions to some of the harder GMAT problems -- Q10, for example, in the diagnostic test at the beginning of OG12 (the one with the pentagram diagram). The solution given in the book introduces 10 unknowns, which is a bit crazy. But since the answers are all numbers (we don't have 'cannot be determined' in the answer choices), that guarantees that the answer is the same no matter how skew or symmetric the diagram; a GMAT question can only have one correct answer, after all. So you can freely assume the pentagon is regular, and thus has interior angles of 108, making all of the triangles isosceles with angles 72, 72 and 36, from which the answer comes immediately; 5*36 = 180.

Note, however, that you could not use this approach on a question like Q179 in the Problem Solving section of OG12; there one of the answers is 'cannot be determined', which means that it is at least possible that the answer may be different depending on what numbers you start with (and indeed, in that question at least, it is different for different starting numbers).

_________________
private GMAT tutor
contact me via the tutor directory at www.gmatix.com
Back to top
View user's profile Send private message
Reply from GMAT/MBA Admissions Expert
lunarpower
GMAT Instructor

Joined: 03 Mar 2008
Posts: 1213

Thanks given: 0
Thanked 221 times in 192 posts

GMAT Score: 800

PostSun Dec 20, 2009 12:00 pm

Quote:
Note, however, that you could not use this approach on a question like Q179 in the Problem Solving section of OG12; there one of the answers is 'cannot be determined', which means that it is at least possible that the answer may be different depending on what numbers you start with
totally true. but you can rest assured that there will be very, very few such problems; after all, there is already an entire half of the quant section (i.e., data sufficiency) dedicated to that exact principle.

also - remember that they will pretty much ALWAYS write problems such that the "gee, i'm going to look at it and think this is the answer" answer is WRONG.
so, if you have a question like the one above - most people would look at it and say, "gee, i think that will probably have multiple values." so, if they take the trouble to include "cannot be determined" into a multiple-choice problem, then something is probably afoot; if the naive guess is "that quantity probably varies", then the quantity most likely doesn't vary. that's pretty much how they write these problems.

_________________
ron purewal

instructor, mgmat

Learn more about me
Back to top
View user's profile Send private message
Reply from GMAT/MBA Admissions Expert
hansoo
MBA Student



Joined: 27 Jun 2009
Posts: 37

Thanks given: 3
Thanked 0 times in 0 posts
Location: Berkeley, CA

GMAT Score: 760

PostTue Feb 02, 2010 2:56 pm

Hey all! I wanted to mention that hackers hacked Magoosh.com 4 months ago. Yet, we've heightened our security tremendously since then and have had no issues with hackers for 4 months. Rest assured that we are legitimate at Magoosh and are serious about keeping your information secure!
_________________
Hansoo Lee
Magoosh - GMAT Prep

MBA Student, Haas
Back to top
View user's profile Send private message
Display posts from previous:   

Post New Topic   Post Reply All times are GMT - 7 Hours
Goto page Previous  1, 2, 3 ... 12, 13, 14
Page 14 of 14
 
Most Active Members in Last 30 Days
1. harsh.champ 625 posts
2. shashank.ism 465 posts
3. ajith 370 posts
4. money9111 353 posts
5. thephoenix 349 posts
Most Active Experts in Last 30 Days
1. lunarpower
Manhattan GMAT Teacher
85 posts
2. Stuart Kovinsky
Kaplan GMAT Teacher
70 posts
3. Lisa Anderson
Stacy Blackman Consulting
50 posts
4. Testluv
Kaplan GMAT Teacher
50 posts
5. Stacey Koprince
Manhattan GMAT Teacher
35 posts