*1. Find out the common factors of the following.*

*(a) 28 & 20*

*(b) 25 & 15*

*(c) 56 & 120*

**SOLUTION: **

(a) Factors of (20) = 1 , 10 , 20, 2 , 4 ,5

Factors of (28) = 7 , 14 , 28 ,1 , 2 , 4 ,

The factors that are common are : 4, 2, 1

(b) Factors of (15) = 1 , 15,3 , 5

Factors of (25) = 1 ,25,5

The factors that are common are : 1 , 5.

(c) Factors of (56) = 1 , 14 , 28 , 56 ,2 , 4 , 7 , 8.

Factors of (120) = 1 ,30 ,40 , 10 ,12 , 2 ,3 ,4 ,5 ,6 ,8 , 15 ,20 ,24 ,60 , 120.

The factors that are common are : 1 , 2 , 4 , 8 .

*2. Find the numbers (all) which are less than 100 and also common multiples of 4 & 3.*

**SOLUTION:**

(*) multiples of 3 = 3, 15, , 6, 9, 12

(*) multiples of 4 = 4 ,8, 12, 16, 20

The Common multiples are = 12, 36, 48,24, 60, 72, 84, 96.

*3. From the given numbers , find which numbers are co prime numbers ?*

*(a) 68 and 17*

*(b) 16 and 81*

*(c) 35 and 18*

**SOLUTION: **

(*) 68 and 17

Factors of 68 = 1, 2, 4, 17, 34, 68

Factors of 17 = 1, 17

The factors that are common are : 1 , 17

Since it has common factors other than 1, the above given 2 number is not a co prime.

(*) 16 and 81

Factors of 16 = 1, 2, 4, 8, 16

Factors of 81 = 1, 3, 9, 27, 81

The common factor is 1. Therefore the given two number is co prime.

(*) 35 and 18

Factors of 35 = 1, 5, 7, 35

Factors of 18 = 1, 2, 3, 6, 9, 18

Common factor is 1. Therefore the given two number is co prime.

*4. A particular number is divisible by both 14 and 5. Find the other number that is always divisible.*

**SOLUTION:**

Factors of 5 = 1 , 5

Factors of 14 = 1, 2, 7

The common factors of these numbers is 1. Therefore, the given two number is co prime number and also the number will be divisible by their product.

*5. A number is divisible by 12. Find the other numbers, which are divisible of 12.*

**SOLUTION:**

The factors are : 1, 2, 3, 4, 6 , 12

Therefore, the numbers 1,2,3,4,6 other than 12 by which this number is also divisible.

*6. Find the common factors of the following given below:*

(*) 4 , 8 and 12

(*) 5 , 15 , 25

**SOLUTION:**

(*) 4 , 8 and 12

Factors of 4 = 1 , 2 , 4

Factors of 8 = 1 , 2 , 4 , 8

Factors of 12 = 1 , 2 , 3 , 4 , 6 , 12

The common factors are : 1, 2, 4.

(*) 5 , 15 , 25

The factors of 5 = 1 , 5

The factors of 15 = 1 , 3 , 5 , 15

The factors of 25 = 1 , 5 , 25

The common factors are : 1 , 5