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confusing kaplan question

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
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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.
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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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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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