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Equations: if abc/72 = 2/d. which of the following expressio

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by II » Fri Aug 22, 2008 12:37 pm
If abc/72 = 2/d. which of the following expressions is equivalent to ab-2 ?

A) 72
B) 72/cd
C) 144/cd
D) a(144-2cd) / cda
E) 144a-2cd / cd

I am more interested in your way of working/thinking than the actual answer itself.

Thanks in advance.
II
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by anju » Fri Aug 22, 2008 12:44 pm
My ans is (144 - 2cd) /cd. I believe E is a typo.
Explanation:L
abc/72 = 2/d
abcd = 144
ab = 144/cd
we need ab-2 so
ab-2 = 144/cd - 2
= (144 - 2cd)/cd
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by leugene » Fri Aug 22, 2008 1:11 pm
Yes, I got that same answer.

But I think it is D then, because you can just cancel out the a's.
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by pepeprepa » Fri Aug 22, 2008 1:29 pm
Except the calculating way, I don't think there is another...

abc/72 = 2/d
abcd=144
ab=144/cd
ab-2=144/cd -2
ab-2=(144-2cd)/cd
ab-2=a(144-2cd) / cda
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by parallel_chase » Fri Aug 22, 2008 1:41 pm
I second pepeprepa's thoughts. This is probably the simplest way to solve this kind of question.

Even if you try to plug in numbers you will be confused with that last step of multiplying "a" to the numerator and denominator.
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by leugene » Fri Aug 22, 2008 2:11 pm
Oops! Unless a=1, haha. Just kidding.

So where is the right answer among the choices? It is not there? I mean, you HAVE to answer the question, right? Better to choose D than nothing.
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by anju » Fri Aug 22, 2008 2:13 pm
leugene wrote:Oops! Unless a=1, haha. Just kidding.

So where is the right answer among the choices? It is not there? I mean, you HAVE to answer the question, right? Better to choose D than nothing.
D is the correct choice.... look for the xplanation above. In you add a to the numerator and denominator, you will get D in the above explanations
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by II » Fri Aug 22, 2008 11:08 pm
Guys.... thanks for input. D is the correct answer.

And E is NOT a typo.
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by II » Sat Aug 23, 2008 12:17 am
anju wrote:
leugene wrote:Oops! Unless a=1, haha. Just kidding.

So where is the right answer among the choices? It is not there? I mean, you HAVE to answer the question, right? Better to choose D than nothing.
D is the correct choice.... look for the xplanation above. In you add a to the numerator and denominator, you will get D in the above explanations
D is multiplying the numerator and the denominator by a ... so it is not actually changing the fraction !

Another way to solve this question would be to plug in numbers ... but it is more time consuming.
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by stop@800 » Sat Aug 23, 2008 4:45 am
Keeping a in num and denom is not right
because the equn does not hold true for a = 0
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by leugene » Fri Aug 29, 2008 12:00 pm
As long as you cancel them out before substituting the real number (0), then it will still work.
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by sumithshah » Sat Sep 06, 2008 10:40 pm
Any one heard Dividendo?

That can be used to solve this

abc / 72 = 2 / d

ab/2 = 72/cd

(ab-2)/2 = (72-cd)/cd

ab-2 = 2*(72-cd)/cd = D

What dividendo basically says is

if a/b = c/d
then a-b/b = c-d/d

Try it if with real numbers or look up here : https://www.tutorvista.com/content/math/ ... erties.php
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