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?
The sum of the probabilities of each of the possibilities must be equal to 1.  This means that the sum of the probability of randomly selecting a red jelly bean, the probability of randomly selecting an orange jelly bean, and the probability of randomly selecting a yellow jelly bean is equal to 1.  If we let the probability of randomly selecting a yellow jelly bean be $x$, then we have \begin{align*}0.2+0.5+x&=1\\\Rightarrow0.7+x&=1\\\Rightarrow{x}&=1-0.7\\\Rightarrow{x}&=0.3\end{align*} Therefore, the probability of randomly selecting a yellow jelly bean from this jar is $\boxed{0.3}$.