Page 13 - 新思维数学活动用书7 样章

1 Integers

1.4 Highest common factors

Worked example 1.4 Key words

a Find the factors of 24. common factor

b Find the highest common factor (HCF) of 24 and 80. conjecture
consecutive
Answer
factor
a 24 = 1 × 24, 2 × 12, 3 × 8, 4 × 6
highest common
The factors of 24 are 1, 2, 3, 4, 6, 8, 12 and 24.
factor (HCF)
b You must find the highest factor of 24 that is also a factor of 80.
8 is a factor of 80 because 80 ÷ 8 = 10.
12 is not a factor of 80 because 80 ÷ 12 = 6 remainder 4.
24 is not a factor of 80.
The highest common factor of 24 and 80 is 8.

Exercise 1.4

Focus

1 Find the factors of:
a 21 b 32 c 50 d 72 e 43
2 Find the factors of:
a 51 b 52 c 53 d 54 e 55

3 a Find the common factors of 16 and 28.
b Find the highest common factor of 16 and 28.

4 a Find the common factors of 30 and 45.
b Find the highest common factor of 30 and 45.

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