very simple problem - hard to crack !!! - The Beat The GMAT Forum

very simple problem - hard to crack !!!

Expert replies

desiguy: Junior | Next Rank: 30 Posts; Posts: 22; Joined: Thu Jul 10, 2008 1:51 pm; Location: london

by desiguy » Tue Jul 15, 2008 11:55 pm

In a formulae a=b(square)c, if b is multiplied by 2 and c is multiplied by 3, what whoudl a be multiplied by ?

4
6
9
12
18

Ans : 12

I know it’s a very very dummbo questin. But my answer is 6. Not sure how its 12 ?

Like this post

Source: Beat The GMAT — Problem Solving | Tue Jul 15, 2008 11:55 pm

sudhir3127: Legendary Member; Posts: 829; Joined: Mon Jul 07, 2008 10:09 pmFollowed by: 3 members; Location: INDIA; Thanked: 84 times

by sudhir3127 » Wed Jul 16, 2008 12:19 am

can i know how u got 6. i got 12 ..

a= b^2c

((2)^2)* 3 = 12

Like this post

desiguy: Junior | Next Rank: 30 Posts; Posts: 22; Joined: Thu Jul 10, 2008 1:51 pm; Location: london

by desiguy » Wed Jul 16, 2008 12:28 am

Thanks...but u assume a and b to be 1 each. I assume the numbers to be different
:
a=2
b=3

(2^2)*3=12.................1
(4*2)*(3*3) = 72..............2

Thus multiply 12 by 6 to get 72 ??

Like this post

sudhir3127: Legendary Member; Posts: 829; Joined: Mon Jul 07, 2008 10:09 pmFollowed by: 3 members; Location: INDIA; Thanked: 84 times

by sudhir3127 » Wed Jul 16, 2008 12:32 am

you cant assume a value for "a" simply becoz its a function of b^2*c ..hence the value of 'a' will always depends on what b and c are...

hope thast helps

Like this post

desiguy: Junior | Next Rank: 30 Posts; Posts: 22; Joined: Thu Jul 10, 2008 1:51 pm; Location: london

by desiguy » Wed Jul 16, 2008 12:34 am

sorryyyyy

replace a & b in my previous answer to b&c. Ie i assume b=2 and c=3. hence the answer of 12.

Like this post

sudhir3127: Legendary Member; Posts: 829; Joined: Mon Jul 07, 2008 10:09 pmFollowed by: 3 members; Location: INDIA; Thanked: 84 times

by sudhir3127 » Wed Jul 16, 2008 12:36 am

on a second thought even in ur example.. u shud take (4^2)* 3*3= 144 and not 72..

so 12*12 = 144 I think u missed whole square and nultiplied by 2 instead.

even then the answer is 12

Last edited by sudhir3127 on Wed Jul 16, 2008 12:37 am, edited 1 time in total.

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

Re: very simple problem - hard to crack !!!

by lunarpower » Wed Jul 16, 2008 12:37 am

desiguy wrote:In a formulae a=b(square)c, if b is multiplied by 2 and c is multiplied by 3, what whoudl a be multiplied by ?

4
6
9
12
18

Ans : 12

I know it’s a very very dummbo questin. But my answer is 6. Not sure how its 12 ?

the easiest way to answer this question is to plug in your own numbers and watch what happens. the setup of the answer choices (i.e., all different positive factors) guarantees that any choice of numbers will uniquely yield the correct answer, unless you're unfortunate enough to have selected 0 as one of the initial numbers.

the easiest choice is: b(initial) = c(initial) = 1. then a(initial) = (1^2)(1) = 1.
then you double b and triple c, which means that b(new) = 2 and c(new) = 3. therefore, a(new) = (2^2)(3) = 12.
a has gone from 1 to 12, so it's been multiplied by a factor of 12.
you should find that the same happens regardless of your initial choice of numbers. if it doesn't, then you have miscalculated something.

--

if you want to prove this formally, do this:
at the start, the formula is (b^2)(c).
after doubling b and tripling c, you have ((2b)^2)(3c) = (4b^2)(3c) = 12(b^2)(c).
the original quantity has been multiplied by 12.

easier to pick numbers, though - no need to deal with messy things like distributing of exponents

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

desiguy: Junior | Next Rank: 30 Posts; Posts: 22; Joined: Thu Jul 10, 2008 1:51 pm; Location: london

by desiguy » Wed Jul 16, 2008 12:48 am

Thank Ron and Sudhir...

Got it!! thanks. Instead of doubling the b and then squaring it, I doubled the squared b !!

S.

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