I’m taking the GRE in a couple days. I’ve always been pretty bad at math, and now that I haven’t actually taken a math class in ten years, I’m dreadful. I’ve spent the last few months frantically studying math, but I sometimes run into problems my prep books don’t clarify enough for me. Not sure of what else to do, I turn to you, the Dopers. I have two questions I cannot figure out for the life of me.
- One of my math prep books states that squaring a negative number not inside parenthesis results in a negative number. So, (-2)²=4, but -2²=-4. This is NOT what I remember from math class, but, like I said, it’s been a long time and even when I was actually taking math, I sucked at it. My OTHER GRE prep book, however, doesn’t say that at all, and in fact includes a practice question that only makes sense if negative numbers outside of parentheses square into positive numbers.
My books are contradicting each other! What should I believe?
- I’ve also got this practice CD-ROM that ETS sent me. There’s a counting principle question in there that just completely baffles me, no matter how many times I read and reread the counting principle section of my prep book. The question is:
You must pick a five person team from a group of twelve people. After picking three members of the team, how many possibile combinations can be made with the last two picks? [This is from memory, so the wording might not sound like an ETS question, but trust me, I have it memorized.]
AFAICT, the number ought to be 72, because with the fourth pick you have 9 possibilites, and with the fifth pick, you have 8. 9x8=72, fin. But the CD-ROM says that the answer is 36 and I CANNOT FIGURE OUT WHY.
Thanks, Dopers!