How do we divide numbers into different groups: square numbers, whole numbers, multiples of 3, factors of 36, numbers less than 21 . . etc? One way is to use inequalities to define a set of numbers that interest us and a set of numbers we happy to leave to one side, for the time being. Your teacher will have given you a number, get ready to move yourself either to the left (the "desired" set of numbers) or the right...