A jar is filled with red, orange and yellow jelly beans.  The probability of randomly selecting a red jelly bean from this jar is $0.2$, and the probability of randomly selecting an orange jelly bean from this jar is $0.5$.  What is the probability of randomly selecting a yellow jelly bean from this jar?
I need to find the probability of selecting a yellow jelly bean, which I will call $p_y$. I know that the sum of the probabilities of all possible outcomes must be equal to $1$, so I can write an equation: $0.2 + 0.5 + p_y = 1$. Solving for $p_y$, I get $p_y = 1 - 0.2 - 0.5 = 0.3$. Therefore, the probability of selecting a yellow jelly bean is $0.3$. 