I prefer to express solutions to inequalities using interval notation. Both formats are are important but I think interval notation is easier to understand and represents better the solutions.
For example, if you have the following inequation:
x-2> 1
x>3
Therefore, the solution could be written either x>3 OR (3, +inf). But what happens if the solution to the system of equation is x>3 or x<-3? The solution can be easily written as: (-inf, -3) U (3, inf) instead of <em>'x>3 or x<-3' </em>which is more confusing.
Whole numbers are similar to natural(non-negative, non-fractional). The only difference is that it includes the 0.
In this question, Rio placed -1 as an example of whole number. Since -1 is negative, it is not a whole number, so this the number which Rio placed incorrectly.