OG12 #116 - A Different Approach? - The Beat The GMAT Forum - Expert GMAT Help & MBA Admissions Advice

OG12 #116 - A Different Approach?

Expert replies

Jim@StratusPrep: MBA Admissions Consultant; Posts: 2279; Joined: Fri Nov 11, 2011 7:51 amFollowed by: 266 members; Location: New York; Thanked: 660 times; GMAT Score:770

by Jim@StratusPrep » Wed Jun 13, 2012 8:34 am

Your first solution works, but you can make it more manageable:

Column 1 -> 0 dots
Column 2 -> 1 dots
Column 3 -> 2 dots
Column 4 -> 3 dots
...
Column 30 -> 29 dots

Essentially you will add the consecutive integers from 1 to 29 inclusive, which is 15 x 29 = 435

Hope this helps

GMAT Answers provides a world class adaptive learning platform.
-- Push button course navigation to simplify planning
-- Daily assignments to fit your exam timeline
-- Organized review that is tailored based on your abiility
-- 1,000s of unique GMAT questions
-- 100s of handwritten 'digital flip books' for OG questions
-- 100% Free Trial and less than $20 per month after.
-- Free GMAT Quantitative Review

Like this post

Source: Beat The GMAT — Problem Solving | Wed Jun 13, 2012 8:34 am

Bill@VeritasPrep: GMAT Instructor; Posts: 1248; Joined: Thu Mar 29, 2012 2:57 pmFollowed by: 192 members; Location: Everywhere; Thanked: 503 times; GMAT Score:780

by Bill@VeritasPrep » Wed Jun 13, 2012 8:34 am

I looked at it differently. If we have 30 cities, how many routes are there between them?

30 (cities for the starting point) * 29 (cities for the ending point; we can't end in the starting city)

However, 30*29 gives us a lot of repeats. It will include both City A to City B and City B to City A. Since we want each distance represented only once, we need to divide by 2:

(30*29)/2 = 15*29 = 435.

Join Veritas Prep's 2010 Instructor of the Year, Matt Douglas for GMATT Mondays

Visit the Veritas Prep Blog

Try the FREE Veritas Prep Practice Test

Like this post

GMATGuruNY: GMAT Instructor; Posts: 15539; Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members; Location: New York, NY; Thanked: 13060 times; GMAT Score:790

by GMATGuruNY » Wed Jun 13, 2012 12:44 pm

Each dot in the mileage table above represents an entry indicating the distance between a pair of the five cities. If the table were extended to represent the distances of 30 cities and each distance were to be represented by only one entry, how many entries would the table then have?

(A) 60
(B) 435
(C) 450
(D) 465
(E) 900

Every PAIR of cities must be represented by a dot.
To determine the number of dots that are needed, we simply need to count how many PAIRS can be formed from the 30 cities.
The number of combinations of 2 that can be formed from 30 options = 30C2 = (30*29)/(2*1) = 435.

The correct answer is B.

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

Like this post

GMAT/MBA Expert

lunarpower: GMAT Instructor; Posts: 3380; Joined: Mon Mar 03, 2008 1:20 amFollowed by: 1535 members; Thanked: 2256 times; GMAT Score:800

by lunarpower » Wed Jun 13, 2012 1:36 pm

Hi,

Of all the solutions I see here, I like the mentality behind this one most:

Jim@StratusPrep wrote:Your first solution works, but you can make it more manageable:

Column 1 -> 0 dots
Column 2 -> 1 dots
Column 3 -> 2 dots
Column 4 -> 3 dots
...
Column 30 -> 29 dots

Essentially you will add the consecutive integers from 1 to 29 inclusive

this is the point: you should be able to LOOK FOR PATTERNS, without needing a memorized "template" or "problem type" for everything on the test.
there are other ways to do the problem, including the combinatorial solutions that some other instructors have offered up on this thread, but pattern recognition is really the name of the game here.

the idea of the book is to contain patterns that are *more common* than others -- but you definitely need to be able to recognize patterns WITHOUT the benefit of "categories" or whatever else.
in fact, you should first look to see whether you can make any intuitive sense of the problem yourself -- i.e., find the patterns without having to bother with classifying the problem. you should really only be classifying the problems if you don't have the requisite intuition.

this is clearly not something we can print in a book -- i.e., we can't write a book that says "the primary point is to get it, but here are some templates/categories if you don't get it when you first look at it". we have to fill the book with objective techniques that people can execute.
but, that's the point. in fact, the point of the entire GMAT, really.

Ron has been teaching various standardized tests for 20 years.

--

Pueden hacerle preguntas a Ron en castellano
Potete chiedere domande a Ron in italiano
On peut poser des questions Ã Ron en franÃ§ais
Voit esittÃ¤Ã¤ kysymyksiÃ¤ Ron:lle myÃ¶s suomeksi

--

Quand on se sent bien dans un vÃªtement, tout peut arriver. Un bon vÃªtement, c'est un passeport pour le bonheur.

Yves Saint-Laurent

--

Learn more about ron

Like this post

gmattesttaker2: Legendary Member; Posts: 641; Joined: Tue Feb 14, 2012 3:52 pmFollowed by: 8 members; Thanked: 11 times

by gmattesttaker2 » Fri Jun 15, 2012 11:10 pm

Jim@StratusPrep wrote:Your first solution works, but you can make it more manageable:

Column 1 -> 0 dots
Column 2 -> 1 dots
Column 3 -> 2 dots
Column 4 -> 3 dots
...
Column 30 -> 29 dots

Essentially you will add the consecutive integers from 1 to 29 inclusive, which is 15 x 29 = 435

Hope this helps

Hello Jim,

I was just wondering why we are taking 15 here. Is it because 15 = 30/2? I just wasn't very clear about the reasoning. Thanks for your help.

Regards,
Sri

Like this post

GMAT/MBA Expert

lunarpower: GMAT Instructor; Posts: 3380; Joined: Mon Mar 03, 2008 1:20 amFollowed by: 1535 members; Thanked: 2256 times; GMAT Score:800

by lunarpower » Sat Jun 16, 2012 4:13 am

gmattesttaker2 wrote:I was just wondering why we are taking 15 here. Is it because 15 = 30/2? I just wasn't very clear about the reasoning. Thanks for your help.

Regards,
Sri

i'm not jim, but he is just using the universal formula for the sum of any set of numbers when the average is known:
Sum = (Average) x (How many numbers)
if you have the numbers from 1 to 29, then there are 29 numbers, whose average is 15.

Like this post

gmattesttaker2: Legendary Member; Posts: 641; Joined: Tue Feb 14, 2012 3:52 pmFollowed by: 8 members; Thanked: 11 times

by gmattesttaker2 » Sat Jun 16, 2012 8:55 pm

lunarpower wrote:
gmattesttaker2 wrote:I was just wondering why we are taking 15 here. Is it because 15 = 30/2? I just wasn't very clear about the reasoning. Thanks for your help.

Regards,
Sri
i'm not jim, but he is just using the universal formula for the sum of any set of numbers when the average is known:
Sum = (Average) x (How many numbers)
if you have the numbers from 1 to 29, then there are 29 numbers, whose average is 15.

Hello Ron,

Thank you very much for the explanation. It is clear now.

Best Regards,
Sri

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

560 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review