Probability (combinatorics) for GRE

[k0dama]

Hi everyone...
I'm studying for the GRE. I've been focusing on English because I thought my Math isn't bad but..
it turns out I don't know anything when it comes to questions about probability.
I need a lot of help to learn how to set these questions up.

Here's a question from studying last night:
A 7-member committee is formed from a pool of 10 people.

Comments

[chipuni]

The first two problems aren't probability. They're called "Combinatorics". There's a good page about that branch of math at mathisfun.com.

I'll help by showing how to think about the first problem:

A 7-member committee is formed from a pool of 10 people. What is the number of the possible outcomes?There's a little trick that will help you figure out this problem. Creating a 7-member committee from a pool of 10 people is exactly the same as creating a 3-member committee from the same pool of 10 people. Why? Because all that you're doing is dividing the group of 10 people into two groups: one with 7 members, and one with 3 members

[k0dama]

Hmm..
so 10*9*8 divided by the number of ways one can organize three people.. 6? 10*9*8/6?

:) I am glad to know this is actually called "combinatorics". It's a great start, and thank you for the website. I'm studying it now!

[chipuni]

Perfect!

And you're welcome.

[just_you_wait]

A similar way to think about it is to put the 10 people in order (e.g. in a row), and pick the first 7 to be in the committee

[jestingrabbit]

For the last question, I'd say you did pretty well, but instead of using 50/100 and 20/100, you could use 1/2 and 1/5, and keep your numbers small.