Prime and Composite Numbers

Prime & Composite Numbers

Definitions you need to know:

Prime Number – is a natural number that has only two natural number divisors; which are 1 and itself.

Composite Number - is a positive integer which has a positive divisor other than one or itself.

Prime Factorization – is a way of finding which prime numbers multiply together to make the original number.

1.) Prime Number Chart:

Below is a chart with numbers going from 1-100. Go through the chart and circle the numbers that are prime numbers and cross out the composite numbers.

Hints:

1. 1 is neither a prime or composite number.
2. No multiple of 2 can be a prime number.
3. Cross out the multiples of your lowest prime numbers.
4. Cross out all multiples of 3.
5. Cross out all multiples of 5.
6. Cross out all multiples of 7.

2.) Find Prime Numbers using Blocks:

Using a type of block method we can find if a number is prime or composite by doing the same as examples above illustrate. Prime numbers are only able to make one square or rectangle where as composite numbers can make multiple squares or rectangles. Below you are presented with multiple numbers, use the blocks given to you by your instructor to find out whether or not those numbers are prime or composite. Write a “C” for composite and a “P” for prime next to the number given.

1. 6

2. 8

3. 5

4. 3

5. 7

3.) Factor Tree Method:

Factor trees are used as a way to find the prime factorization of a number. Below is an example of a factor tree and how it works.

We can see that the factors of the number 90 are highlighted in blue and that by multiplying these numbers together we can see they equal 90, therefore these are the factors of 90. Now that you have an idea of how factor trees work try to find the prime factorization of the numbers below by putting all prime factors in the circles.

4.) The Ladder Method:

In this method we use a design similar to division problems, a slightly different method than the factor tree but with the same results. In the illustration above the factors are once again highlighted in blue and by multiplying these numbers together we can see they equal 75, therefore these are the factors of 75. Now that you have an idea of how the ladder method works try to find the prime factorization of the numbers below using the ladder method.