M3.1.5 For the adult
Prime numbers
Why can 7 stones go in only one row, but 6 stones can make two rows?
What this chapter teaches
A prime number has exactly two factors, 1 and itself. The number 1 is not prime. To find the primes up to 100, cross out the multiples of 2, 3, 5 and 7 and keep what is left.
Three questions to ask
There is no one right wording. Listen for the idea.
- Why can 7 stones only go in one row, but 6 stones can go in two?
- Is 91 prime? How can you tell?
- Why is 2 the only even prime?
After the chapter, the learner can
- Say if a number up to 100 is prime
- Find all primes up to 100 by crossing out multiples
What they copy into their notebook
A prime has exactly two factors, 1 and itself. 1 is not prime. 2 is the only even prime. There are 25 primes up to 100. For a number from 2 to 100, test with 2, 3, 5 and 7.