The Venn diagram shows the probabilities associated with three events $S$, $T$ and $U$, representing materials found in a recycling center. The probability of a sample containing only $S$ is 0.2, only $T$ is 0.05, and only $U$ is 0.25. The intersection $S\cap T$ is $q$ and $T\cap U$ is $p$. There is no overlap between events $S$ and $U$. The probability of a sample containing none of these materials is $r$.