Question

Is $18$ prime or composite?

Answer 1

Hint:To find whether $18$ is a prime or composite number we need to know what prime numbers and composite numbers are. Prime numbers are those numbers which have exactly two integral divisors, $1$ and the number itself whereas composite numbers are those numbers which have more than two integral divisors. So, in this question we have to check the divisibility of $18$ by different numbers.

Complete step by step answer:
A prime number has exactly two factors- $1$ and the number itself.For example: The number $5$ is a prime number because it can only divide by $1$ and the number itself means it has only two factors: $1$ and $5$. A composite number has at least three factors.For example: The number $4$ has three factors $1,2$ and $4$ as it can be divided by $1,2$and $4$.

Now we will check whether $18$ is a prime number or a composite number. For a prime number it should have only two factors: $1$ and $18$ itself but for composite numbers it should have more than two factors. $18$ can be divided by $1,2,3,6,9$ and $18$. So, the factors of $18$ are $1,2,3,6,9$ and $18$. As $18$ has more than two integral divisors.Hence, $18$ is a composite number.

We can also say that a composite number is a positive integer that can be formed by multiplying two smaller positive integers. For example, the integer $10$ is a composite number because it is the product of the two smaller integers $2 \times 5$. Likewise, $18$ is also a composite number as it can be formed by multiplying two smaller positive integers i.e., $2 \times 9,\,3 \times 6$.

Hence, $18$ is a composite number.

Note:Prime numbers are considered as the numbers which have only two factors i.e., one and the number itself. Note that all prime numbers are odd numbers apart from $2$ and $2$ is the smallest prime number. Composite numbers are those numbers that have more than two factors and they are further divided into odd composite numbers and even composite numbers. Odd composite numbers are those numbers which do not have $2$ as a prime factor whereas even composite numbers are those numbers which have $2$ as a prime factor.