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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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Brent Hanneson - GMAT Prep Now instructor
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