Unit 9 Contents

1. Find the next number that is not circled or crossed out. What number is it?
2. Is this a prime number?
3. Circle this number. Cross out all of the multiples of this number up to 100.
4. Are any of these numbers prime? How do you know?
4. Continue the steps in Question 3 until you have only prime numbers left on your chart. List all the prime numbers from 1 to 100.
1. As you made your chart, what patterns did you see?
2. What digits do prime numbers end in?
3. Are prime numbers ever next to each other? Why or why not?
4. Twin primes are pairs of prime numbers that are separated by only one number. For example, 5 and 7 are twin primes. Can you find any other twin primes?
1. Use your sieve. Is 43 prime or composite?
2. Show or tell how you can explain your answer to someone without using your sieve. (Remember: A prime number is a number with exactly two factors, one and itself.)
1. Is 39 prime or composite?
2. Show or tell how you can justify your answer using the definition of a prime number.

Check-In: Questions 8–10

8. Use the 200 Chart to help you make the following two lists:
1. List the multiples of 3 from 30 to 60.
2. List the multiples of 7 from 35 to 98.
9. List all the factors of the numbers below. You may use your lists from Question 8 and a calculator to help you.
1. 37
2. 42
3. 51
4. 53
10. Which of the numbers in Question 9 are prime? Justify your answers using the definition of a prime number.

Continue your investigation of prime numbers by finding all the prime numbers between 101 and 200.