Q:

Is 9 a prime number?

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Quick Answer

Nine is not a prime number. It is a composite number, because it has more than two factors. A prime number is only divisible by one and by itself, and nine is divisible by one and by nine, but it is also divisible by the number three.

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Full Answer

One way of understanding the difference between prime numbers and composite numbers is to visualize a rectangle of a given area. Since the area of a rectangle is found by multiplying length times width, the length and width can be understood as the possible factors of the area. If the area is a prime number, there can be only one set of whole number dimensions possible. For example, a rectangle with an area of seven must have sides of one and seven. If the area is a composite number, then there can be numerous solutions. For example, if the area is nine, then the rectangle could have sides of one and nine or three and three.

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