Answer:
or 0.2632 or 26.32%
Explanation:
Choosing a white or a yellow marble from the bag are two mutually exclusive events. So we can say that:

To get the probability of each we divide the favorable outcomes by the all possible outcomes.
Probability of choosing white:

Probability of choosing yellow:




If you need it in decimal, just divide and you will get 0.2632.
If you need it in percent, just multiply the decimal by 100% and you will get 26.32%.