Welcome! My name is Kevin coming from Magoosh
today we're talking a little bit about data sufficiency problems on the GMAT
and specifically um a trap that you should avoid. Something that causes students some problem
on the test are their assumptions so that's why I've written "beware of your assumptions". Don't
be lazy, don't jump into a problem and just assume that you know what's going on, because
the GMAT's tricky, they make problems a little bit tricky and they're looking for lazy students. So
let me grab my pen here and let me show you what I mean. So imagine that you have this question on
the test, "what is the value of x?" It's test day, I'm taking the test, I know I need to keep moving ,
I look at this question right all right I gotta solve for x. I look I see I have two
linear equations with two values, I know that if I have two variables and I have two questions- two
linear equations with those variables I can solve for any one of those variables and I'm like all
right I just need both of these C moving forward. But you just got that question wrong because
of assumptions, you're making too many assumptions. Yes, you have two variables, and yes you have two
linear equations and usually yes that means you can figure out what the value of one of those
variables are but let's work this problem and see why that's not true. So we can quickly eliminate
a couple of answer choices. So I can see in statement one I'm not going to be able to
figure out what x is what x what the value of x is excuse me because I still have this y so
eliminate a look at statement 2 again. Same thing have two variables I'm not going to know which
what the value of x is with that y in there. This is where you need to pay attention, together you
think oh I can solve for these together and get the value of x, but let's work statement
1 and see if we can make it equal to y and see what happens. So if we come over here, 5x plus 3y
equals 15 okay so that's statement 1. Let's move our 5x over so minus 5x
minus 5x so now I have 3y equals 15 minus 5x am I in the way can you see this. Okay, now I
can divide by 3 on both sides, right. Now I have y equals five minus five thirds x look
this is the same as this so now I know that they're giving us just the same information
and two different statements just looks different but it's actually the same thing. So you're not
actually getting two different linear equations, you have the same one just written differently.
So both of these problems together are definitely not going to work I know because a and b didn't
work then d is not correct and so e here is the correct answer. So on the test beware
of your assumptions, don't let them uh lead you to taking a shortcut to the wrong answer. Do enough
work to be certain that you have the right answer. You can do this fairly quickly, um just don't rush
through it and you'll be okay. So with data sufficiency beware of what they're giving you
they might be trying to trick you! All right that's all I have uh if you have any questions about the
GMAT or data sufficiency questions drop them in the comments below I'd be happy to answer them.
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material that's also fun. All right be excellent to the universe and I will see you next week.