**Which of these numbers are prime?**

30,31,32,33,34,35,36,37,38,39,40

In this example 31 and 37 are prime.

A shortcut to see if a number is prime is to follow these rules.

**Step 1.**Find the square root of the number.

For example, the square root of 36 is 6.

**Step 2.**Find the prime factors of the square root.

For 6 = 2 and 3

**Step 3.**If the original number is divisible by these prime numbers then it is a composite number, if it is not divisible then it is prime.

36 is divisible by 2 and 3 so it is a composite number.

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