Probability the Bowl is Empty When the Last Orange is Drawn

James has a bowl containing $s \geq 1$ strawberries and $o \geq 1$ oranges. He draws fruits one at a time, uniformly at random without replacement, and stops as soon as there are no oranges left in the bowl. What is the probability that the bowl is completely empty when he stops? Evaluate for $s = 10$, $o = 20$.