Prime numbers up to 100 KS2 Revision
What you need to know
Things to remember:
- You need to know the prime numbers between 1 and 20
- 1 isn’t a prime number
- 2 is the only even prime number
A prime number is a positive whole number bigger than 1 that only has two factors, itself and 1.
For example, 13 is a prime number because its only factors are 1 and 13.
You need to learn the prime numbers between 1 and 20:
2 3 5 7
11 13 17 19
2 is a special prime, because it is the only even prime. All other even numbers can be divided by 2, so can’t be prime.
You need to be able to tell if a number smaller than 100 is prime.
Is 59 a prime number?
If you can’t divide a number less than 100 by 2, 3,5, or 7 and get a whole number, then it is prime.
59\div2=29.5
59 \div 3 = 19.6666...
59 \div 5 = 11.8
59 \div 7 = 8.42…
59 is a prime number!
Example Questions
Question 1: Is 19 a prime number?
19\div2=9.5
19 \div 3 = 6.333...
19 \div 5 = 3.8
19 \div 7 = 2.714…
19 is a prime number.
Question 2: Is 42 a prime number?
42\div2=21
42\div 3 = 14
42 \div 5 = 8.4
42\div 7 = 6
42 is not a prime number.