Lesson 1: Factors and Multiples

Math 10C Module 2 Lesson 1

Module 2: Roots and Powers

Discover

The Greek mathematician Eratosthenes, who lived in North Africa around 230 BC, invented a simple way of determining prime numbers called the Sieve of Eratosthenes. Complete the Try This to see how this method works.

Try This 1

Download and print the 100 Grid sheet. Then complete each step.

Step 1: Cross off the number 1 since it is not prime.

Step 2: Circle the number 2, but cross off all multiples of 2 (4, 6, 8, 10, and so on) that are on the grid.

Step 3: Circle the number 3, but cross off all multiples of 3 (6, 9, 12, 15, and so on) that have not already been crossed off on the grid.

Step 4: Look at the next uncrossed number. Circle it and cross off its multiples on the grid.

Step 5: Repeat step 4 until all numbers are either circled or crossed off.

Answer the following questions:

1. How many numbers remain?
2. What do you notice about the numbers that are remaining?
3. How is this method useful?
4. How can you use this method to create a secret code?

Check your answers using the link below.

Possible TT1 (Try This 1) Solutions