1/ One of the many great things about Pi is that it's algorithmically compressible. You can express the idea of Pi using far fewer characters than are actually contained in its numerical expression (which would be an infinite number). #PiDay

Between 0 and 10 (say), there are an infinite number of rational numbers: those expressible as p/q, where both p and q are integers. The rationals are "dense" - given any number between 0 and 10, there is a rational number arbitrarily close to it. 2/