Sub. :- Mathematics

Divisibility

Std. :- 5th

Chapter no. 5

Test of divisibility by 2

2,4,6,8,10,12,14,18,20,22,26,................,are multiples of 2. All these numbers are divisible by 2. All these numbers have either o,2,4,6, or 8 in the unit place.

Number which have 0,2,4,6,or8 in the units place are divisible by 2.This is the test of divisibility by 2

Examples :-

Which of the numbers 304,288,43,764,200,811,76,222,907,544 are divisible by 2 ?

Test of divisibility by 55,10,15,20,25,30,35,40,45,50,.......................are all multiples of 5. We find only 0 or 5 in the units place of these numbers. These numbers are divisible by 5

Number which have 0 or 5 in the units place are divisible by 5.This is the test of divisibility by 5

Examples :-

Which of the numbers 304, 200,15, 195,307,755,85,49 are divisible by 5 ?

Test of divisibility by 1010,20,30,40,50,.....................100,120,.......................have 0 in the units place. They are divisible by 10.

Number which have 0 in the units place are divisible by 10 . This is the test of divisibility by 10

Examples :-

Which of the numbers 300, 200,1550, 195,305,7550,80,49 00 are divisible by 10?

Test of divisibility by 3

3,6,9,12,15,18,21,24,27,,................,are multiples of 3. All these numbers are divisible by 3. The sum of the digits of these numbers is a multiple of 3 .

When the sum of the digits of a given number is divisible by 3 ,the number is divisible by 3 . This is the test of divisibility by 3

Examples :-

Which of the numbers 154,4353,4356,6235,285, are divisible by 3?

Prime numbers and composite numbers

Prime numbers :-The numbers which have only 1 and the number itself for factors.Such numbers are called Prime numbers.

Composite numbers :- The numbers which have more than two factors.Such numbers are called composite numbers

Note :- 1 is neither a prime nor a composite number. 2 is the smallest prime number

Classify the following numbers into prime numbers & composite numbers.

25,5,38,42,87,31,91,18,47,13,69,97