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GMAT Prep - PS Ratio & Proportion

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GMAT Prep - PS Ratio & Proportion

by albertrahul » Tue Jul 01, 2008 9:22 pm
I'm not sure I understand GMAT answer here, please help me understand that.

My solution:
Let History Majors = 10

English Majors (Twice of History) = 20

Maths Majors (Three times of English) 20*3 = 60

So ratio of History to maths = 10:60 = 1:6

What is incorrect here, please explain.
My answer is ofcourse incorrect :(
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by microke » Tue Jul 01, 2008 10:57 pm
Let history majors =x
so,English majors =2x -Eqn(1)

Let maths majors =y
So english majors =3y -Eqn (2)

Using equations (1) and (2) y=2x/3

History: Maths = x:y =x: 2x/3 i.e. 3:2

The right answer is 3 to 2
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Re: GMAT Prep - PS Ratio & Proportion

by beeparoo » Wed Jul 02, 2008 9:42 am
albertrahul wrote:I'm not sure I understand GMAT answer here, please help me understand that.

My solution:
Let History Majors = 10

English Majors (Twice of History) = 20

Maths Majors (Three times of English) 20*3 = 60 <--This is where you screwed up. "Eng majors are 3 times as many as Math majors", which means that E = 3*M or M = 20/3.

So ratio of History to maths = 10:60 = 1:6

What is incorrect here, please explain.
My answer is ofcourse incorrect :( Now you know why. Turn that frown upside-down!
~Sandra
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by albertrahul » Wed Jul 02, 2008 7:18 pm
Thank you both :)
I shall read questions more carefully.
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by ksh » Wed Jul 02, 2008 11:06 pm
microke wrote:Let history majors =x
so,English majors =2x -Eqn(1)

Let maths majors =y
So english majors =3y -Eqn (2)

Using equations (1) and (2) y=2x/3

History: Maths = x:y =x: 2x/3 i.e. 3:2

The right answer is 3 to 2
Hi microke,
I think your answer is reversed

HM=2EM
MM=3EM

So, HM/MM=2/3

am i wrong?
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by albertrahul » Wed Jul 02, 2008 11:12 pm
OA is B :)
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by microke » Thu Jul 03, 2008 1:31 am
ksh:

A ratio in general should not involve fractions. For example, 1:1/3, though it not incorrect to express like this, it always mathematically correct to represent any ratio in integers:

1:1/3 is written as 3:1....by multiplying three on both sides of the fraction....hope it clarifies your doubt....
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