Finding Primes Activity (Sieve of Eratosthenes)

There is a way to find prime numbers that was used by the ancient Greeks. See if you can follow the reasoning.

A Visual Method for Finding Prime Numbers

Question 1)

We crossed out the number 1 in Step 1. How do we know that 1 is not a prime number?

Question 2)

In Step 3, we crossed out the multiples of 2 (that were bigger than 2). How do we know these numbers are not prime?

Question 3)

List all of the prime numbers between 1 and 100.

Question 4)

A lot of the numbers ending with the digit 1 are prime. However, 51 is not a prime number.[br]List all the factors of 51 and explain why it is not a prime number.

Question 5)

In our example, we could stop with the multiples of 7. Can you explain why?[br](Hint: It depends on the size of the grid).

Information: Finding Primes Activity (Sieve of Eratosthenes)