Page 1 - Activity

SAI International School
Math Lab Activity-2

TOPIC: Prime and Composite Numbers

OBJECTIVE:

To identify the prime numbers and composite numbers.

PRE-REQUISITE KNOWLEDGE:

 The numbers whose only factor is 1 and the number itself are called prime number.
 The numbers which are having more than two factors are called composite numbers.

MATERIALS REQUIRED:White paper, colour pencil or sketch pens.

ACTIVITY:
 Without actually checking the factors of a number, we can find prime numbers from 1 to
100 with an easier method.
 This method was given by a Greek Mathematician Eratosthenes, in the third century
B.C.
 Let us see the method. List all numbers from 1 to 100, as shown below.


 Step 1 : Cross out 1 because it is not a prime number.
 Step 2 : Encircle 2, cross out all the multiples of 2, other than 2 itself, i.e. 4, 6, 8
and so on.
 Step 3 : You will find that the next uncrossed number is 3. Encircle 3 and cross
out all the multiples of 3, other than 3 itself.
 Step 4 : The next uncrossed number is 5. Encircle 5 and cross out all the multiples
of 5 other than 5 itself.
 Step 5 : Continue this process till all the numbers in the list are either encircled or
crossed out.