[music introduction]
[wheel rolling]
Yahoo!!!
[feet shuffle]
a circle can be a lot of fun, but its useful
too
as you'll soon see
Let's review a little bit now
If you remember
A prime number is a counting number that has
exactly 2 factors
one and itself
an example is the number 3
It has 2 factors, one and 3
A composite number has more than 2 factors
For example
the number twelve has factors of 1, 2, 3,
4, 6, and 12
Take a good look
Do the numbers 3 and 12 have any common factors
That is
do they share any of the same numbers
This is where the circle can be mighty useful
A venn diagram has 2 or more overlapping circles
It is often used in mathematics to show relationships
between groups or sets of numbers
The factors of one number go in the outer
portion of the left circle
The factors of the other number go in the
outer portion of the right circle
Any common factors are brought into the overlapping
section of the two circles
As you can see
the numbers 3 and 12 both share the factors
1 and 3
Now we can look at something a little more
complicated
Let's compare a set of numbers and a composite
number
In this case we need to look at all prime
numbers less than 20 on the left
and the composite number 30 on the right
The prime numbers less than 20 include
2, 3, 5, 7, 11, 13, 17 and 19
The factors of 30 include
1, 2, 3, 5, 6, 10, 15, 30
as you can see, the common factors are
2, 3, and 5
Are you ready for some practice?
Label the left circle Prime Numbers less than
15 and the right circle Factors of 21
Place all the prime numbers less than 15 into
the left circle
and all of the factors of 21 into the right
circle
Don't forget that any shared numbers will
go into the overlapped area of the 2 circles
[pause]
How'd you do?
The Prime numbers less than 15 are
2, 3, 5, 7, 11 and 13
Factors of 21 are
1, 3, 7, and 21
Shared numbers are 3 and 7
these should be inside the overlapping area
[rain, thunder, lighting]
Uh-oh
I knew I should have brought an umbrell-
