**Divisibility Rules Workbook-1**

When we multiply a number by 1, 2,3, 4, etc. The products are known as multiples of the numbers.

**Important points :**

1. A number is a multiple of itself.

2. Every number is multiple of 1.

3. Multiples of a numbers are either greater than or equal to the number.

4. There are infinite multiples of a number.

**Divisibility rules :**

A number will be divisible by 2 if the digit at the unit place is divisible by 2.

A number will be divisible by 3 if the sum of digits of the number is divisible by 3

A number will be divisible by 4 if the last two digits of the number together are divisible by 4.

A number will be divisible by 5 if digit at the unit place is either 0 or 5.

A number will be divisible by 6 if the digit at the unit place of the number is divisible by 2 & sum of all digits of the number is divisible by 3.

Divisibility test of 7: Make two set of three nos. starts from unit digit then add the alternate sets, and find out the mutual difference, if it is 0 or any multiple of 7 then the given no. is divisible by 7.

A number will be divisible by 8 if the last 3 digits, all together, is divisible by 8.

A number will be divisible by 9 if sum of all it’s digits is divisible by 9.

Read More...**Factorisation of Numbers Workbook-1**

Factors are the numbers that are multiplied to give a product.

If a number ‘a’ is divided by ‘b’ and remainder is zero than ‘b’ is said to be factor of ‘a’

**Co-Prime Numbers:**

Two numbers (not necessarily prime) are co-prime, if they have only 1 as common factor.

e.g., (1, 2), (1, 3), (3, 4), (3, 10), (3, 8), (5, 6), (7, 8) etc.

These numbers are also called as relatively prime numbers.

**Note:**

(a) Two distinct prime numbers are always co-prime but converse need not be true.

(b) Consecutive numbers are always co-prime numbers.

**Twin Prime Numbers:**

If the difference between two prime numbers is two, then the numbers are called as twin prime numbers. e.g., {3, 5}, {5, 7}, {11, 13}, {17, 19}, {29, 31}.

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