2. Lesson one 1) Counting numbers : Fifth Primary The Numbers Any numbers you can use for counting things: 1, 2, 3, 4, 5, ……………….. It is usually represented by letter C Notes : Does not include zero or negative numbers or fractions or decimals. Book P. 2 &P. 3

3. 2) Natural numbers : The counting numbers + zero. It is usually represented by letter N Notes : Does not include negative numbers or fractions or decimals. Remarks:  N = the set of counting numbers  { 0 }.  N – {0}= the set of counting numbers.  The set of counting numbers is  the set of natural numbers.

4. Remember The set of counting numbers = { 1, 2, 3, 4, ……..} or C = { 1, 2, 3, 4, ……..} It is an infinite set The set of Natural numbers = { 0, 1, 2, 3, ……..} or N= { 0, 1, 2, 3, ……..} It is an infinite set  The smallest natural number is zero.  The smallest counting number is one  C  N  N – {0}= C  N ∩ C = C

5. Solved Examples 1)Complete by using , ,  or  : A. ɸ ……………….. C B. {12526 } ……………….. N C. 0 ……………….. C D. {1.5 } ……………….. N E. 9.25 + 0.75 ……………….. C A.  B.  C.  D.  E.  Solution:

6. 1)Complete by using , ,  or  : A. ɸ ……………….. N B. {0} ……………….. C C. 0 ……………….. C D. {1, 0.5 } ……………….. C E. {125684 }……………….. N 2)Complete :

7. 3) Put (√) or (×): I. 0.5 is a natural number between 0 and 1 ( ) II. The set of the natural number is finite set ( ) III. 7.5  C ( ) IV. {0 }  {1, 2, 3, 4 } =N ( ) Homework Booklet P.1 and P. 2