Exercise 1.2
Multiples, factors and primes
1 Find the first three multiples of each number. a 12 b 15 c 32 2 From the numbers in the box, find: a a multiple of 10 c a common factor of 27 and 36
d 50
b two factors of 24 d a prime number.
8
9
12
23
32
40
98
99
100
3 List all the prime numbers between 40 and 50. 4 Which of the numbers in the box is: a a multiple of 2 b a multiple of 5 c a common multiple of 2 and 5 d a factor of 500 e a prime number f a common multiple of 2 and 3?
95
17, 37 and 47 end in 7 and are prime numbers, so 57 and 67 must also be prime numbers.
6 Write true (T) or false (F) for each statement. a 7 is a factor of 84. b 80 is a multiple of 15. c There is only one prime number between 90 and 100. d 36 is the lowest common multiple (LCM) of 6 and 9. e 5 is the highest common factor (HCF) of 25 and 50. 7 Find the LCM of each pair of numbers. a 4 and 6 b 15 and 20 c 20 and 50
d 6 and 7
8 Find the factors of each number. a 27 b 28 c 72
d 82
e 31
9 Find the prime factors of each number. a 32 b 18 c 70
d 99
e 19
10 Find the HCF of each pair. a 12 and 15 b 12 and 18
d 12 and 25
11 The HCF of 221 and 391 is 17. Explain why 221 and 391 cannot be prime numbers. 12 Find two numbers that are not prime and have a HCF of 1.
8
1 Integers, powers and roots
97
You may use some numbers more than once.
5 Is Mia correct?
c 12 and 24
96