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ChartWorld Tutorial

Helping Students Learn Multiplication & Division

 

1 - Introduction

2 - Getting Started

3 - Basic Functions

4 - Skip Counting

5 - Repeated Addition

6 - Arrays

7 - Factors

8 - Commutative Property

9 - Division

10 - Fact Families

11 - Division with Remainder

12 - Prime Numbers

13 - Feedback

12 - Prime Numbers
 
A prime number is an integer that cannot be evenly divided by any other integer except 1 and itself. In other words, a prime number has no other factors except 1 and itself. For example, 7 can only be evenly divided by 1 and 7, so we say that it is a prime number. (By the way, all prime numbers must have exactly two factors so by definition 1 is not a prime number since its only factor is 1.)

Ask the students how we can test which numbers are prime using ChartWorld.

Let's start with the number 2. We are not allowed to click on the number 1 nor the number 2, so 2 must be a prime number.

How about 3? Since we aren't allowed to click on 1 or 3, the only number we can click on is 2.

Notice that after we clicked on 2, the number 3 is not colored, therefore it is also a prime number.

Moving to the next number, we see that 4 is already colored because 2 is a factor of 4. This means that the number 4 is not a prime number. Instead the number 4 is called a composite number, which means that it has more than two factors (in this case 1 and 4, as well as 2).

The next number to check is 5. The numbers 2 and 4 are already colored, so let's click on 3 (be sure to change the ink color using the F12 key for each number).

After clicking on 3, the number 5 is still not colored. This means that it is a prime number.

How about the number 6? Notice that is is colored in both orange and blue. This means that it is a composite number with the factors 2 and 3, as well as 1 and 6. In fact, all of the "stacked" numbers (colored in both orange and blue - 12, 18, 24, etc.) are multiples of 6.

Up to this point, we have determined that the numbers 2, 3, and 5 are prime numbers and the numbers 4 and 6 are composite numbers.

Let's continue on to the number 7. Remember, we cannot click on the number 1, so let's click on the only blank number less than 7. Click on the number 5.

Notice that 7 is still not colored, so 7 must also be a prime number. Also notice that the number 30 is "stacked" with the colors orange, blue, and green. This is because 2 x 3 x 5 = 30. The multiples of 30 have all three colors.

Finally, let's click on the number 7 to find the rest of the composite numbers.

The prime numbers under 100 are: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, and 97.

With some programming to ChartWorld, we can also show the prime numbers like this...

Notice that all of the prime numbers are in white this time and that the number 1 is colored in black.

 

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  Questions? Email dekendiz@fau.edu