To determine if 20 is a prime number or a composite number, we simply look at the factors for 20.
If the factors of 20 are only 20 and 1, then we know that 20 is a prime number. Otherwise, 20 is a composite number.
To explain better, if 20 is only divisible by 1 and 20, then it is a prime number, and if 20 is divisible by more than 20 and 1, then it is a composite number.
The factors of 20 are as follows:
1, 2, 4, 5, 10, 20
Therefore, since 20 is divisible by more than one and itself, the answer to the
question "Is 20 prime or composite?" is highlighted in blue below.
composite
Is 21 prime or composite?
OK. Now you know that 20 is a composite number. Use our logic above and see if
you can figure out if the next number on our list is prime or composite before you check your answer.
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