The scope of this video lesson consists in studying the sets of Rational and Irrational numbers. The main objectives for the students are: 1) Learning how to distinguish between a rational number and an irrational number; 2) Learning about the existence of 2 infinities: the "countable infinity" for sets of Rational numbers and the "uncountable infinity" for the set of irrational numbers; and 3) Learning to use straightforward and advanced tools from Mathematics to reach goals (1) and (2). [43:13]