What is the probability that Glen will get a yellow marble?  Express answer as a percent.

Probability is  calculated by creating a ratio and dividing the numerator by the denominator to create a decimal and then a percent.

For example:

2 cars are green and 3 cars are red.  What is the probability that the car that is chosen is red?

favorable (what you want picked)  = 2   = .4  =40%
         total  number of choices           5