Lesson: Common GMAT Data Sufficiency Myths - Part II

Rate this video: 
5

Comment on Common GMAT Data Sufficiency Myths - Part II

hello again :)

another question, when we are dealing with a quadratic and we know that only positive numbers fulfil our conditions (for instance in geometry), could we skip the calculation in this case? or is it also possible to get 2 positive solution from a quadratic ?
gmat-admin's picture

Yes, it's possible to get to two positive solutions to a quadratic equation.

Take, for example, x² - 5x - 6 = 0
Factor to get: (x - 2)(x - 3) = 0
So, x = 2 or x = 3

Cheers,
Brent

Hello admin... From the question x and y are both positive integers how did u take x and y as 1
gmat-admin's picture

Is this the question you're referring to: https://gmatclub.com/forum/if-x-and-y-are-positive-integers-what-is-the-... ?

If so, I'm not sure what you are asking. I don't have x = 1 and y = 1 as a solution anywhere in my answer (https://gmatclub.com/forum/if-x-and-y-are-positive-integers-what-is-the-...)

Can you please elaborate on your question?

Cheers,
Brent

You assumed the statement is sufficient by taking x=1 and y=1 because the statement said x and y are positive integers. I think it is insufficient because you can have other positive integers that will make the equation not sufficient such as 2 ,3 4 etc. can you explain ?
gmat-admin's picture

I believe you're referring to the question that starts at 2:15 in the above video.

We're told that x and y are positive integers, and we want to determine the value of x.

STATEMENT 1 tells us that 10x + 5y = 15
When we simplify this equation, we get: 2x + y = 3

Keep in mind that, in Data Sufficiency questions, each statement is true, so it MUST be the case that 2x + y = 3

Since there is ONLY ONE pair of values that satisfy this equation (x = 1 and y = 1), we can be certain that x MUST EQUAL 1.

If you feel that x could have values other than 1, you must find a DIFFERENT pair of x and y values that satisfy the equation 2x + y = 3.

For example, you are suggesting that x could equal 2. However, in order to satisfy the given equation (2x + y = 3), we must find a POSITIVE value of y to go along with x = 2.
However, if x = 2, then y must equal -3, and -3 is not positive.

Does that help?

Cheers,
Brent

Add a comment

Tweet about our course!

If you're enjoying our video course, help spread the word on Twitter.

Change Playback Speed

You have the option of watching our videos at various speeds (25% faster, 50% faster, etc). To change the playback speed, click the settings icon on the right side of the video status bar.

We can help

Once you’ve scheduled your course, let us know, and we’ll help you promote it

Free “Question of the Day” emails!