Factors, Powers And Standard Form Worksheet Page 6
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21E
5
Show that 20 can be written as the sum of two prime numbers in
two different ways.
2
AO
Highest common factors
The highest common factor (HCF) of two numbers is the largest number that is a factor of
both numbers.
The factors of 12 are 1, 2, 3, 4, 6 and 12.
The factors of 16 are 1, 2, 4, 8 and 16.
Another way to fi nd
HCFs is covered in
The common factors of 12 and 16 are 1, 2 and 4.
Section 10.5.
So the highest common factor of 12 and 16 is 4.
Example 5
C
What is the highest common factor of 20 and 30?
Write down the factors of both numbers and circle the common factors.
Remember to include 1
Factors of 20: 1 , 2 , 4, 5 , 10 , 20
and the number itself in
Factors of 30: 1 , 2 , 3, 5 , 6, 10 , 15, 30
your list of factors.
The common factors are 1, 2, 5 and 10.
The highest common factor is 10.
Exercise 10E
D
1
a
Write down the factors of 12.
HCF stands for highest
b
Write down the factors of 8.
common factor.
c
What is the HCF of 12 and 8?
C
2
Work out the highest common factor of
a
15 and 25
b
14 and 12
c
21 and 15
d
24 and 20
e
8 and 10
f
8 and 16
3
Write down two numbers larger than 10 with an HCF of 8.
C
72 cm
4
Lydia is making Christmas decorations. She needs
to cut identical squares out of a rectangular sheet
of paper.
a
What is the largest square size Lydia can use
60 cm
without wasting any paper?
2
AO
b
How many of these squares will Lydia be able to
cut from this sheet of paper?
10.2 Factors and primes
163
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