Abag contains 6 red marbles, 6 white marbles, and 4 blue marbles. find p(red or blue).

Probability (P) is basically outcome, and chance. What are the chances of grabbing a red or blue marble? 
Well, there IS a more complicated way to solve this, but let's go the easy way.
You calculate probability with this equation:
Probability=Events/Number of outcomes
If you want to find the probability of grabbing a red or blue marble, you first have to find all possible outcomes by adding ALL numbers together. 6+6+4=16. Next, find how many events you have. Well, you want to find red or blue. Add the number of red and blue marbles together. 6+4=10, so your equation now looks like: Probability=10/16
Now, just simplify.
10/16 can be divided evenly by 2 on both sides, so just do that, and you get:
5/8
You have a 5/8 chance, or a 0.625 chance of drawing a red or blue marble.