Videos to help Grade 4 students explore the properties of prime and composite numbers to 100 by using multiples.

Common Core Standards: 4.OA.4

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Lessons for Grade 4

Common Core For Grade 4

1. Follow the directions.

Shade the number 1 red.

a. Circle the first un-marked number.

b. Cross off every multiple of that number except the one you circled. If it’s already crossed off, skip it.

c. Repeat Steps (a) and (b) until every number is either circled or crossed off.

d. Shade every crossed out number in orange.

2. List the circled numbers.

a. Why weren’t the circled numbers crossed off along the way?

b. Except for the number 1, what is similar about all of the numbers that were crossed off?

c. What is similar about all of the numbers that were circled?

1. A student used the Sieve of Eratosthenes to find all prime numbers less than 100. Create a step-by-step set of directions to show how it was completed. Use the word bank to help guide your thinking as you write the directions. Some words may be used just once, more than once, or not at all.

2. What do all of the numbers that are crossed out have in common?

3. What do all of the circled numbers have in common?

4. There is one number that is neither crossed out nor circled. Why is it treated differently?

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