In math we use various types of numbers. Though you will study more as you get older, the following groups (or systems) include most of the numbers we will work with. Natural numbers are also known as the "counting numbers". They are the group of numbers that we count with. The lowest of these numbers is 1. The group is as follows: {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, . . . } There is no highest number in the natural numbers group (the group approaches infinity). Whole numbers are all non-negative numbers that do no have a decimal or fractional portion. To be non-negative simply means to not be negative. Therefore, whole numbers are not negative. The least of these numbers is 0. The group is as follows: {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, . . . } There is no greatest number in the whole numbers group (the group approaches infinity). Notice that 0 is the only difference between the whole numbers and natural numbers groups. Integers are all numbers that do nt have a decimal or portion. Sometimes they are described as both positive and negative whole numbers. There is no least or greatest of the integers. The group is as follows: { . . . , -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5, . . . } If you take all the whole numbers and make them both positive and negative, you end up with the integers group. Rational numbers are all numbers that can be written as a fraction of two integers. The rational numbers group includes all integers as well as terminating and repeating decimals. This group includes most of the numbers that we are familiar with at this point. Later, we will study others. Terminating decimals are those that end (termintate). Repeating decimals are those that repeat. Decimals that do not repeat, but yet do not terminate (e.g. pi) are not included in the rational numbers group. Examples:       Irrational numbers are numbers that are not rational. In other words, they are numbers that CANNOT be written as a fraction of two integers. Another way to think about these numbers is to keep in mind what type of decimals they are. Since rational numbers are all the terminating and repeating decimals, irrational numbers are all the numbers that do not terminate and do not repeat. That means, irrational numbers are decimals that never end and never repeat. At this point, there is only one number we know of thats like this - pi (Π). Although when using 3.14 it seems that pi terminates, it is important to remember that this is just an estimate for pi (as is 22/7). There are other numbers in this group as well, but it is too early at this point to mention them. We will return to this group during our discussion of exponents and roots. The important thing to note is that this group does not include any other number discussed so far, only pi. A real number is any rational or irrational number. The real number group is just a collection of all numbers that are rational and numbers that are irrational. In other words, every number that we have seen or worked with is a real number. There are numbers that are not real numbers. No, they are not called 'fake' numbers, but if your were thinking 'imaginary' you might be on the right track. :o)   Venn Diagram A Venn diagram allows us to visual see the relationship that one or more groups/entities has. This Venn diagram shows the relationship between the 6 number groups we've looked at. From the diagram we see that the smallest group of numbers is the Natural numbers. We also see that the Natural nubmers circle is completely inside the Whole Numbers circle. It is drawn this way to show that every Natural number is a Whole number. Since there is space leftover inside the whole numbers circle, it means there must be one or more whole numbers that are not natural. Zero is the only number that would be considered a whole number, but not a natural number. Since the whole numbers circle is inside the Integers circle, we have shown every whole number is an integer. However, there is still space leftover inside the integers circle for the numbers that are integers, but not whole. This space is reserved for the negative integers (e.g. -2, -3, -4, etc.). The ingegers circle is completely inside the rational numbers rectangle. This means all integers are rational. There is room leftover inside the rational numbers rectangle for all those numbers that are rational, but not considered integers. This space is reserved for all values with fractional portions (e.g. 1.25, -2.3, etc.). The irrational numbers rectangle is not inside, nor does it overlap the rational nubmers rectangle. This means they share no common numbers. If a number is inside the rational numbers group, then it cannot be a part of the irrational numbers group, and vice versa. However both rectangles are inside the entire Real numbers rectangle (made from both smaller rectangles). This means all rational numbers and irrational numbers are real numbers. However, you'll notice there is no space leftover. This means that Real numbers are only rational or irrational. No other type of number is considered Real.