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## Plugging In! Is it efficient?

tagged by: Brent@GMATPrepNow

This topic has 1 expert reply and 0 member replies
Mochad Just gettin' started!
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Plugging In! Is it efficient? Sun Mar 25, 2012 1:35 pm
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Hi,

How far is Plugging In technique efficient in algebra problems? And do you recommend other techniques?

Best wishes,
Mochad

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Brent@GMATPrepNow GMAT Instructor
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Thu Mar 29, 2012 9:24 am
Mochad wrote:
Hi,

How far is Plugging In technique efficient in algebra problems? And do you recommend other techniques?

Best wishes,
Mochad
I'm assuming that "Algebra Problems" are the same as "Variables in the Answer Choices" questions.

I would say that plugging in is not as efficient as solving these questions algebraically. Plugging in can take a LOT more time.

For example, consider this rudimentary question.

Joe has J dollars and Mona has M dollars. If they combine their money, how much will they have?
A) J+M
B) JM
C) J-M
D) J/M
E) J^M

The Plug-In method tells us to choose some values for J and M.
Let's say that J=2 and M=2.
When J and M have these values, Joe's and Mona's combined wealth is 4 dollars.

Now we need to plug J=2 and M=2 into each answer choice, and see which one evaluates to be 4.

A) 2+2=4 (bingo)
B) (2)(2) = 4 (bingo)
C) 2-2 = 0 (nope - eliminate it)
D) 2/2 = 1 (nope - eliminate it)
E) 2^2 - 4 (bingo)

Hmmm, it looks like the correct answer is A, B or E

At this point, we need to plug in some different numbers to whittle the field down to just one correct answer. For example, if we let J=5 and M=2, we can see that only answer choice A yields a combined wealth of 7 when we plug J=5 and M=2 into the expression.

So, in this example, plugging in works, but it can take a lot of time.
The fastest way to solve these questions is the apply some reasoning and algebra.

Cheers,
Brent

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