Page 100 - Start Up Mathematics_4

Common Factors Remember

To find the common factors of two or more numbers, find The biggest factor that is common
the factors of each number. Then identify the common to all given numbers is called
factors. the highest common factor
or HCF of the given numbers.
Example 6: Find the common factors of 6 and 18.

Solution: 6 18

2 3 2 9

3 3

Factors of 6 are 1, 2, 3 and 6.
Factors of 18 are 1, 2, 3, 6, 9 and 18.
So, the common factors of 6 and 18 are 1, 2, 3 and 6.

EXERCISE 7.1

1. Write down the factors of the following numbers.

(a) 28 (b) 50 (c) 48 (d) 90 (e) 36
2. Make a factor tree for the following numbers.

(a) 18 (b) 32 (c) 96 (d) 40 (e) 54
3. Find the common factors of the following numbers.

(a) 8 and 12 (b) 9 and 15 (c) 12 and 50

(d) 6, 15 and 42 (e) 20, 35 and 60 (f) 8, 12, and 16
4. Write the first 10 prime numbers.

5. Write ‘T’ for true and ‘F’ for false statements.
(a) The smallest prime number is 1.

(b) 7 is a prime number.
(c) The smallest factor of every number is 1.

6. Express the following composite numbers as a product of their prime factors. Use
division method.
(a) 108 (b) 124 (c) 100 (d) 275 (e) 240

Multiples
Consider the multiplication 5 × 6 = 30.

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