Lesson: Intro to GRE Quantitative Comparison (QC)

Comment on Intro to GRE Quantitative Comparison (QC)

I'm very relieved to have found this course. It's like a healthy shot of WD40 working on the rust in my math-brain. Thank you very much!
greenlight-admin's picture

I'm glad you like it!

The best set of online resources for GRE i have come across till date . It's a 5/5 for the content , would recommend to all :)
greenlight-admin's picture


tahmina.mm's picture

I am so glad, i found this.


when i solved many QC problem, literally if found no question having E as answer? is it very rare in actual GRE?
greenlight-admin's picture

Quantitative Comparison question have only 4 answer choices:

A) The quantity in Column A is greater.
B) The quantity in Column B is greater.
C) The two quantities are equal.
D) The relationship cannot be determined from the information given.

So, E can never be the correct answer of a Quantitative Comparison question.

My blunder sorry! i was suppose to say D.
greenlight-admin's picture

I wouldn't say that it's rare for the correct answer to be D on an Quantitative Comparison question.

How is it possible that x= -5? -5^2 does not equal to a positive 25. I know i'm missing a step here, can someone explain this to me?
greenlight-admin's picture

Hi Ruby,

You're referring to the question that appears at 3:20 in the video.

The given information tells us that x² = 25

x = 5 is one solution, since 5² = (5)(5) = 25

x = -5 is another solution, since (-5)² = (-5)(-5) = 25

For more on multiplying positive and negative numbers, see the following video: https://www.greenlighttestprep.com/module/gre-arithmetic/video/1059

its really a relevant effort made by greenlighttestprep. its the only one, i can say, all in one regarding GRE preparation. excellent work is done and quality is there.
greenlight-admin's picture

Thanks Shahbaz!

In the question where the heights of Glen and Kayla are involved they didn't mention that Glen height is always <= 70 it can be >70 too in that case the correct option is 'D' and sorry if my interpretation is wrong.
greenlight-admin's picture

Hi Suhas,

You're referring to the question that starts at 2:10 in the above video.

The key here is that their heights add to 140 inches AND Kyla is taller than Glen.

For example, Kyla could be 72 inches tall, and Glen could be 68 inches tall.

Or Kyla could be 70.5 inches tall, and Glen could be 69.5 inches tall.

Or many other scenarios.

Now let's say for a moment that Kyla is 67 inches tall. This means Glen is 73 inches tall (to get a sum of 140 inches). HOWEVER, this does not meet the condition that Kyla is taller than Glen. So, it CANNOT be the case that Kyla is 67 inches tall.

Try finding some other values for their heights, and you'll find that Kyle will ALWAYS be more than 68 inches tall. In fact, she will always be taller than 70 inches.

Does that help?


Hi Brent,

I am further along the course but somehow ended up on this page again. In a later lesson, you mentioned that GRE only cares about the positive values for square roots. For example, sq rt of 25 = + 5 and - 5, however, since GRE only cares about the positive value (+ 5), won't the answer for the last example in this video be A? Please let me know. Thanks.
greenlight-admin's picture

You're referring to the question at 3:20 in the video.

Keep in mind that the original question does not have any square root signs.

The square root NOTATION tells us to take the POSITIVE square root of a number.
So, for example, √9 = 3, √25 = 5 and √49 = 7

Conversely, the equation x² = 25 does not feature any square root notation.
In this case, there are TWO SOLUTIONS: x = 5 and x = -5

If we want to formalize this outcome we can write:
If x² = k, then there are two possible solutions: x = √k and x = -√k

Does that help?


Yup, that cleared things up. Thank you!

Hey Brent,
It's so good to learn from you. I am enjoying, videos are consistent. Please attach more practice under each video.

greenlight-admin's picture

Thanks for the kind words!
I add new practice questions to the course everyday.

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