Roster Method ( Listing Method ) :   Under this method, we just make a list of  the objects of  the set and put them within braces { }.

 e.g. (i) If  A is set of  first five prime numbers, then A  =  { 2, 3, 5, 7, 11, }

  (ii) If  B is the set of  all counting numbers between 100 and 400, then

B  =  { 100, 101, 102, 103, . . . , 399, 400 }.

Set Builder Form ( Property Method ) :   This method consists in listing the properties common to all the elements of  the set.

We write, { x / x has properties P }  or   { x : x has properties P }.

 e.g. (i) If  A is the set of  all natural numbers less than 8, then we write,

A  = { x / x   N, x < 8 }.

  (ii) If  B  =  { 4, 7, 10, 13, 16 }, then we can write :

B  =  { x : x  =  3n + 1, where n  N, n < 6 }.

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