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What is a Prime Number?

Maths | 6-13 yrs | Interactive, Learning Pod

Prime Number – Facts and Examples

A prime number is a whole number greater than 1; but it can be divided only by 1 and the number itself.

For example:
Let us take the number 6.
The number 6 can be divided evenly by 2 or 3.
2×3= 6

Let us take another number, say 5.
The number 5 cannot be divided evenly.
1×5= 5

Thus, a prime number is a number which:

  • Is greater than 1.
  • Cannot be divided evenly.
  • The only two factors of the number are 1 and the number itself.

The numbers which are not prime numbers are called composite numbers.

Can you divide 8 apples evenly among 4 children?
4×2= 8; each child gets 2 apples.
4 and 8 are composite numbers.
Can you share 7 apples evenly among 4 children?
No, because 7 is a prime number.

Steps to prove whether a number is a prime number or not

  • Try dividing the number by 2. See if you get a whole number. If you do, it cannot be a prime number.
  • Try dividing the number by prime numbers like 3,5,7,11. If it is divisible by prime numbers then it is not a prime number.

For example:
9 is divisible by 3 but not divisible by 2; thus 9 is not a prime number.
15 is divisible by 3 and 5 but not divisible by 2; thus 15 is not a prime number.

Cool math for kids

  • Number 1 is neither prime nor composite.
  • The largest prime number known has 13 million digits!
  • Type the prime number 379009 on a calculator and read it upside down. It will read as Google!
  • There are an infinite number of prime numbers.

Exercise

  1. Write down all numbers from 1 to 100 in rows of 10 each.
  2. Cross out 1 because it is not a prime number.
  3. Cross out all multiples of 2.
  4. Cross off multiples of prime numbers found in the first row, like 3, 5 and 7.
  5. All the numbers left are prime numbers.

For more interesting Maths worksheets and lessons, go to : http://mocomi.com/learn/maths/

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