If c and d are integers, is c even? GMATPrep - DS

[RonPurewal]

If both c and d are odd, statement 2 cannot possibly be true.

Odd + 2 and odd + 4 are still odd. Odd times odd is odd.

Yes, you are right. I goofed up my first grade math :(

There's a way to fix this:
Write down EVERY step of EVERYTHING. All the time, every time.

I've had students who didn't want to do this because they "felt dumb".
Studies show, though, that people commit 40 to 50 errors in mental math for every one error in written math. So, a 97.5-98% reduction in your error rate shouldn't make you feel too dumb!

[RonPurewal]

Also—
In just about every case, writing down the steps is FASTER than trying to do them in your head. (This is the other common excuse for not writing down the steps—"I thought it would take too long.")

Try it!