You randomly choose one of the marbles. Without replacing the first marble, you choose a second marble. There are 4 marbles. One yellow, one red, one green, and one blue. Find the total number of possible outcomes.

6 Possible outcomes.
this is a combination problem the order of drawing a marble is not important because red, blue would be the same outcome as blue, red. 
the combination formula is as follows.
[tex]nCr= \frac{n!}{r!(n-r)!} [/tex]
plug in 4 for n and 2 for r.
[tex]nCr= \frac{4!}{2!(4-2)!} =6[/tex]