These numbers are always small, and you need to keep them accurate to several decimal places. There is nothing to worry about. Lecture Terminology Experiments with just two possible outcomes occur quite often. For instance, a medical doctor is interested whether his patient will live through the operation - an experiment with two outcomes. A social scientist may be interested if people stuck on a remote island feel happy.
Proportions are fractions .
Since all decimal numbers can be written as fractions, this procedure is often extended to expressing all decimal numbers. Percents are often used to express both probabilities and sample proportions. These two uses are really a bit different. Once we talk about samples, we should also say what are the populations. This is not quite the same.