Prime numbers, factors & multiples

Identify prime numbers, find factors and multiples, and recognise prime factors

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1
Which of these is a prime number? A) 1 B) 4 C) 7 D) 9
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2
Write the first multiple of 6 that is greater than 20. First multiple of 6 over 20 is ___
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3
Is this statement true or false? 2 is the only even prime number. A) True B) False
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4
Which of these is NOT a factor of 12? A) 1 B) 3 C) 5 D) 12
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5
Match each number to whether it is prime or not. Match each item on the left to one on the right. Left: 11, 15, 17, 21 Right: Prime, Not prime, Prime, Not prime
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6
How many factors does 16 have? List them as: ___ Factors of 16: 1, 2, 4, ___, 16
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7
Order these prime numbers from smallest to largest: 13, 2, 19, 7. Put these in order: 13, 2, 19, 7
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8
How many prime numbers are between 10 and 20? A) 2 B) 3 C) 4 D) 5
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9
Find the smallest prime factor of 35. Smallest prime factor of 35 is ___
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10
Is this statement true or false? 27 is a prime number. A) True B) False
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Answer key

Prime numbers, factors & multiples · for parents and teachers

1
7
7 only has factors 1 and 7, so 7 is prime. (1 is not prime; 4 = 2×2; 9 = 3×3.)
2
24
The multiples of 6 are 6, 12, 18, 24, 30. The first one over 20 is 24.
3
True
All other even numbers have 2 as a factor (in addition to 1 and themselves), so 2 is the only even prime.
4
5
Factors of 12 are 1, 2, 3, 4, 6 and 12. 5 is not a factor of 12.
5
11 → Prime; 15 → Not prime; 17 → Prime; 21 → Not prime
11 and 17 are prime. 15 = 3 × 5 and 21 = 3 × 7, so they are not prime.
6
8
Factors of 16 are 1, 2, 4, 8 and 16.
7
2, 7, 13, 19
From smallest to largest: 2, 7, 13, 19.
8
4
The primes between 10 and 20 are 11, 13, 17 and 19. That is 4 primes.
9
5
35 is not divisible by 2 or 3, but 35 ÷ 5 = 7. So 5 is the smallest prime factor.
10
False
27 = 3 × 9, so 27 has factors other than 1 and itself. It is not prime.