# Thread: Help with probabilities and combined events.

1. ## Help with probabilities and combined events.

I am studying for the GMAT, but in the midst of taking notes have run across some instructions I just cannot figure out. I have taken Stats, so this will be a refresher, but it seems I forgot tons of stuff I learned in the class.

Here is the instructions given.

For the number cube, if E is the event that the outcome is an odd number, {1, 3, 5}, and F is the event that the outcome is a prime number, {2, 3, 5}, then P(E and F) = P({3, 5}) = 2/6.

Okay, I get hitched where the equatiion includes P({3, 5}). Why is there a 5 in there? It seems that there are 3 odd number, {1, 3, 5}, and 3 prime number, {2, 3, 5}, so why wouldn't the equation read, P({3, 3})?

Thanks for the help!

2. ## Re: Help with probabilities and combined events.

Originally Posted by Stoneface
For the number cube, if E is the event that the outcome is an odd number, {1, 3, 5}, and F is the event that the outcome is a prime number, {2, 3, 5}, then P(E and F) = P({3, 5}) = 2/6. Why is there a 5 in there? It seems that there are 3 odd number, {1, 3, 5}, and 3 prime number, {2, 3, 5}, so why wouldn't the equation read, P({3, 3})?
AND is just intersection.
$E=\{1,3,5\}~\&~F=\{2,3,5\}$ so $E\cap F=\{3,5\}$.

3. ## Re: Help with probabilities and combined events.

So, it is just an intersection. Thanks!