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Key
Idea
If
you know how
many
factors a
whole
number has,
you
can tell if the
number
is prime
or
composite. |
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Vocabulary
•
prime numbers
•
composite
numbers
•
rectangular
array
•
prime
factorization |
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Materials
•
hundred chart |
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Prime
and Composite
Numbers
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How
can you tell if a number is
prime
or composite? |
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Numbers
such as 2, 3, 5, 7, and 11 have a special
property
that many numbers do not have.
Mathematicians
call these numbers prime
numbers.
A prime
number has exactly two different factors,
itself
and 1. |
A
whole number greater than 1 that has more than
two
factors is called a composite number. |
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5
is an example of a prime number. It has only two
factors,
1 and 5. It has only one rectangular
array. |
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6
is an example of a composite number. Its factors are
1,
2, 3, and 6. It has more than one rectangular array. |
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To
determine if a number is prime or composite, you can
use
divisibility rules to help you test possible factors. |
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| Is
141 prime or composite? |
141
is NOT divisible by 2
because
it is odd. |
141
is divisible by 3 because
1 + 4
+ 1 = 6 and 6 is divisible
by 3. |
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141 is composite. |
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| Is
84 prime or composite? |
84
is divisible by 2 because it
is even. |
| So,
84 is composite. |
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 | Talk
About It |
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1.
How is a prime number such as 17 different from
the
numbers in Example A and B? |
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