Question: What Must Be True?

Comment on What Must Be True?

Regardless of p, assuming q is even or odd then:
q-1 or q-2: one of the two has to be even.
Thus, the result must be even.

Is this correct?
gmat-admin's picture

That is correct, devroy. Great work.

Hi, quick question; the expression you evaluated to 0, are you using the foil method? :S is there a quick way you are doing it? thanks, ps love the site.
gmat-admin's picture

I'm just plugging in 2 for an even value and 1 for an odd value, and then performing the necessary calculations.

HOWEVER, once I see that one of the pieces in the product equals zero, I immediately know that the final result will equal zero.

For example, when we plug in 2 for p and q in the first expression, we get 2(2-2)(2-1)
Once I recognize that 2-2 = 0, then we have 2(2-2)(2-1) = 2(ZERO)(2-1), which means the final product will be zero.

understood. thanks :)

Hi Brent,

Thanks for the great videos. I was wondering if we should look to choose numbers that make the equation equal zero or should we try to avoid them? Can this be a trap for some question is what I was concerned about?
gmat-admin's picture

I'm glad you like the videos, Harshbir!
What equation are you referring to?

Sorry, I was referring to the equation in the question: p(q-2)(q-1)
gmat-admin's picture

For me, it's much easier to test (plug in) nice even and odd numbers (like 0's and 1's) than it is to use E's and O's and then have to apply the different rules for even and odd numbers.

Add a comment

Office Hours

Have questions about your preparation or an upcoming test? Need help modifying the Study Plan to meet your unique needs? No problem. Just book a Skype meeting with Brent to discuss these and any other questions you may have. 

Change Playback Speed

You have the option of watching the 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.

Have a question about this video?

Post your question in the Comment section below, and I’ll answer it as fast as humanly possible.

Free “Question of the Day” emails!