Question: Evaluate Expression with 37’s

Comment on Evaluate Expression with 37’s

If I let a=37, then a^2-23a-a-15a; I don't get the same answer, why?
gmat-admin's picture

What answer are you getting when you evaluate the expression?

Hi if i let x=37, I get the expression x^2 -23x - x - 15x
then, x^2 - 38x - x
then, x^2 - 39x
then, x(x-39)
which gives me 0 and 39 as possible values for x when I put the equation = 0

I chose 0 because its one of the answer choices. I know its wrong from the video but could you explain why.
gmat-admin's picture

The small error you just made is very common.

Once you saw got to the EXPRESSION x(x-39), you transformed it into the EQUATION x(x-39) = 0.

However, there is no such EQUATION.
We still need to find the VALUE of x(x-39) when x = 37

So, we must take x(x-39) and replace the x's with 37's
We get: 37(37-39)
Simplify to get: 37(-2)
Evaluate to get: -74

Does that help?

Cheers,
Brent

Add a comment

Tweet about the course!

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

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!