The growth in Software Product Lines (SPLs) created a need for good and fast algorithms to analyze them. Extracting information, such as the number of products, may be crucial to generate a good test suite. However, due to the combinatorial complexity of SPLs, such algorithms may be intractable. Here, we focus on Feature Diagrams, and we use the tree structure to show linear time algorithms to compute the variation degree (number of products) and the commonalities (number of products containing each feature). We use the variation degree to show a uniform sampling procedure of configurations allowed by a feature diagram.