prime

Everyday

1. In maths, a prime number is a whole number greater than 1 that can only be divided exactly by 1 and itself. tree →
2. Prime means main or most important. tree →
3. Prime means of the best quality. tree →
4. Someone's prime is the time when they are strongest or best. tree →
5. To prime something means to get it ready, for example to put a first coat on wood before painting. tree →

In the lessons

Maths: the prime numbers start 2, 3, 5, 7, 11, 13, 17, 19, 23, 29; 2 is the only even prime; 1 is not prime. A number with more factors is composite. Every whole number above 1 is a prime or can be made by multiplying primes (prime factors). Government: the Prime Minister leads the government in the UK, Ireland, Canada, Australia and New Zealand. Phrases: prime number, prime factor, prime minister, prime example, in his prime.

Examples

• 7 is a prime number because only 1 and 7 divide it. tree →
• Is 9 prime? No, 3 × 3 = 9. tree →
• The prime factors of 12 are 2, 2 and 3. tree →
• The Prime Minister spoke on the news. tree →
• This is a prime example of good teamwork. tree →
• The athlete was in her prime. tree →
• Prime the wall before you paint it. tree →
• 2 is the only even prime number. tree →
• The Witch-Queen is put to death, and Nikita lives happily as the King's Prime Minister. tree →

Note

Maths trap: 1 is NOT a prime number (it has only one factor). 2 IS prime even though it is even. To test if a number is prime, try dividing by the primes smaller than it; if none divide exactly, it is prime. «Prime» in «Prime Minister» means first or chief.