confusing kaplan question

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resilient: Legendary Member; Posts: 789; Joined: Sun May 06, 2007 1:25 amFollowed by: 6 members; Location: Southern California, USA; Thanked: 15 times

by resilient » Sun Apr 06, 2008 5:52 pm

I never really came across a question like this befor and am a bit confused. I have a great handle on ratios but I dont even understand the question here.

21. the ratio of x to 4 is 5/12.

What is the ratio of x to 5?

a.1/3
b.1/2
c.25/48
d.2
e.3

Appetite for 700 and I scraped my plate!

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Source: Beat The GMAT — Problem Solving | Sun Apr 06, 2008 5:52 pm

Stuart@KaplanGMAT: GMAT Instructor; Posts: 3225; Joined: Tue Jan 08, 2008 2:40 pmFollowed by: 614 members; Location: Toronto; Thanked: 1710 times; GMAT Score:800

Re: confusing kaplan question

by Stuart@KaplanGMAT » Sun Apr 06, 2008 9:17 pm

Enginpasa1 wrote:I never really came across a question like this befor and am a bit confused. I have a great handle on ratios but I dont even understand the question here.

21. the ratio of x to 4 is 5/12.

What is the ratio of x to 5?

a.1/3
b.1/2
c.25/48
d.2
e.3

x/4 = 5/12

multiplying both sides by 12, we get:

3x = 5

dividing both sides by 5, we get:

3x/5 = 1

dividing by sides by 3 we get:

x/5 = 1/3... choose (a).

There are a lot of other ways you could have played with the ratio to get that final answer.

Stuart Kovinsky | Kaplan GMAT Faculty | Toronto

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ritz: Senior | Next Rank: 100 Posts; Posts: 59; Joined: Sat Mar 08, 2008 5:15 pm; Location: Cincinnati; Thanked: 3 times

by ritz » Mon Apr 07, 2008 5:14 pm

another way is...
given x/4 = 5/12

you have to find x/5
what you are doing actually is, adding 1 to the denominator.
adding 1 to 4 increases it by 25%
so the other denominator will also increase by 25% which is 3
so the result will be 5/15 = 1/3.

this is little more complex but the fundamental behind this is...
when we add or substract any number to the numerator or denominator of a ratio, we are increasing/decreasing it by a certain %. The resultant ratios need to be increased or decreased correspondingly.

regards
Ritz

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GMAT_crusher: Junior | Next Rank: 30 Posts; Posts: 25; Joined: Mon Mar 31, 2008 6:09 pm

by GMAT_crusher » Mon Apr 07, 2008 6:38 pm

Another way is the simple - if x gives y then z gives (z/x)*y

if x/4 gives 5/12, then x/5 gives ((x/5)/(x/4))*5/12
i.e

(4/5)*(5/12) = 1/3

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