# A Quick Look Back

Okay. Let's look at the different sets of numbers before we look at some special ones.• Real Numbers: All the numbers on a number line in any direction, positive or negative.

• Natural Numbers: All of the positive whole numbers without zero. {1, 2, 3, 4, 5, ...}

• Whole Numbers: Natural numbers and zero. {0, 1, 2, 3, 4, ...}

• Integers: All of the whole numbers on the number line and their opposites. {... -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5, ...}

• Rational Numbers: Any number that can be expressed or rewritten as a fraction with two integers. You can't have 0 as the denominator of the fraction.

# Prime Numbers

That's a pretty long list of possible numbers. We haven't included all of the numbers yet, but you have enough to work with for the next few sections. Within those**sets**and

**groups**of numbers, you will find some special ones.

**Prime**numbers are a special group of whole numbers. A prime number is a number that can only be divided by

**one and itself**with no remainder. When we talk about the divisors of a prime number, we are always talking about natural numbers (whole numbers greater than 0).

Examples of Prime Numbers: 2, 3, 5, 7, 11

•

**Can a negative numbers be a prime number? No.**Negative numbers are not natural numbers. That means no fractions either.

•

**Can zero be a prime number? No.**You need two divisors to make a prime. While zero can be divided by any number, you cannot divide by zero.

•

**Is one a prime number? No.**You need two divisors to make a prime (one and itself). Technically, one only has one divisor and is not a prime number.

Let's look at a prime number like 13 for a moment. If you divide 13 by either 1 or 13, you are good. It's a nice and easy division problem with no remainders. If you try to divide 13 by 5, you get a remainder of 3. It doesn't matter what you try, the only two numbers that will work are 1 and 13. The only factors of 13 are 1 and 13. Therefore, 13 is a prime number.

• Ways to get 13: (1x13) or (13x1)

• Factors of 13: 1, 13

Let's look at 14 now. If you divide 14 by either 1 or 14, you get nice even answers. What about other numbers? Let's start with 2. 14÷2 is 7. That means 2 and 7 divide into 14 without a remainder. The numbers 2 and 7 show there are four factors of 14. Since 14 has more than two factors, 14 is not prime. You could say that two whole numbers other than 1 and 14 can be multiplied together to make 14. Therefore, 14 is a composite number.

• Ways to get 14: (1x14), (14x1), (2x7), (7x2)

• Factors of 14: 1, 2, 7, 14 (take a look - there are only two prime factors)

# Before We Go...

•**Is 0 a prime number? No.**0 is neither a prime nor a composite number.

•

**Is 13 real, natural, whole, rational, and prime? Yes.**Since it is rational, it is also an integer.

•

**Is 14 real, natural, whole, rational, and prime? No.**14 is a composite number, because two numbers other than 1 and itself can be multiplied to make 14 (2 and 7).

- Overview
**Number Types**- Factors
- Fractions
- Decimals
- Percentages
- Estimation
- Ratios
- Money
- Activities
- More Maths Topics

# Useful Reference Materials

**Wikipedia:**

*https://en.wikipedia.org/wiki/Fraction_%28mathematics%29*

**Encyclopædia Britannica:**

*http://www.britannica.com/topic/fraction*

**University of Delaware:**

*https://sites.google.com/a/udel.edu/fractions/*