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If a number has only two different factors, 1 and itself, then the number is
said to be a prime number.
7 is a prime number since it has only two different factors.
Note:
But 1 is not a prime number since it does not have two different factors.
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Composite Numbers
- A number that has more than two factors is called a composite
number.
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 - So, 14 is a composite number as it has more than two factors.
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Note:
1 is considered neither a prime number nor a composite number.
Example 10
State which of the following numbers are a prime:
a. 46
b. 19
Solution:
a. 46 is not a prime because 46 = 2 × 23.
b. 19 is a prime since it has only two different factors, 1 and 19.
Example 11
Express 210 as a product of prime numbers.
Solution:
Note:
We try the prime numbers in order of their magnitude.
Example 12
Express 90 as a product of prime numbers.
Solution:
Alternatively, we can use a factor tree to express 90 as a product of
prime numbers as illustrated below.
Key Terms
prime number, composite
numbers, factor tree
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