 We all know what numbers are. And negative numbers. But did you know that mathematicians classify numbers into different types? Into a number system. Let's start at the top with real numbers. They can be positive, negative, zero, decimals, fractions, pi. Nearly any number you can think of is a real number. Only imaginary numbers, like the square root of negative one, and infinity, aren't real. But we don't really need to worry about them at this stage. If you can put a number on a number line, then it's a real number. This symbol is used to represent real numbers. Real numbers split into two subsets. Rational and irrational. Rational numbers can be written as a fraction. I just remember rational-fractional sound similar. So any whole number, terminating decimals, recurring decimals. In fact, all numbers except for non-repeating decimals are rational. Decimals that do not repeat are irrational. Some well-known examples are pi, e, and square root two. So many square roots and cube roots are irrational. If the decimal places go on forever without repeating, then they are irrational. Now back to rational numbers. These can be separated down further. Natural numbers and integers. The integers are any positive whole numbers. Negative whole numbers, zero. Whereas natural numbers are just from zero and the positive counting numbers. Strangely, there is no general agreement amongst mathematicians about whether to include zero in the natural numbers or not. Sometimes zero is included. Sometimes it isn't. If zero isn't considered a natural number, then a whole new category is needed called whole numbers, which is exactly the same as natural numbers, but also includes the zero. Find a way of remembering the order. I always remember now what is real. And then you just need to remember the irrational numbers and the general name, real numbers. Answer these questions, making sure to include all that apply. Pause the video, answer them, and click play when you're ready. Now we just need to know that this real number system exists and why are different numbers fit into it? If you stick with mathematics in future life, you may study it in more detail. As I said earlier, I always just remember now what is real to remember the order of natural numbers, whole numbers, integers, and rational numbers. If you liked the video, give it a thumbs up, and don't forget to subscribe, comment below if you have any questions. Why not check out our Fusechool app as well? Until next time!