Lesson Plan : Prime Numbers

Teacher Name:
 Matthew Masters
 Grade 5

 Prime Numbers
 Prime Numbers, Composit Numbers, Factors, Sieve of Eratosthenes
 Students will be able to identify numbers less than or equal to 100 as prime and composite numbers.
 Standards Florida Sunshine State Standards MA.A. The student knows if numbers (less than or equal to 100) are prime or composite. Florida Process Standards Numeric Problem Solvers 03 Florida students use numeric operations and concepts to describe, analyze, communicate, synthesize numeric data, and to identify and solve problems.
 -One overhead transparency of the 100 Number Chart (See Attached File) -One overhead marker -A highlighter marker for each student -Pencils -A sieve, strainer, or colander of any kind -Chalkboard/chalk OR white board/marker(s)
 1. Present the class with your colander/sieve. Lead the class in a discussion of its uses as a cooking strainer, or a sand sifter. Emphasize that what is LEFT in the sieve is our object of interest today. 2. Tell the class that they are going to throw the numbers from 1-100 in their own sieves and sift out all but some special numbers! Introduce Eratosthenes as a famous Greek mathematician from thousands of years ago. Explain how Eratosthenes developed this procedure to find these special numbers. 3. Review the terms multiple and factor. Write examples from students on the board. 4. Lead a short class discussion of the relationship between multiples and factors.
 5. Introduce the term prime number, present examples on the board, and discuss what makes them prime in terms of the number of factors. 6. Lead the students to name the first four prime numbers and write them on the board (2,3,5,7). 7. Hand out the 100 Number Chart (See Attached File) and a highlighter to each student. 8. Direct the students to highlight the first four primes that are written on the board AND THEN PUT THE HIGHLIGHTER AWAY FOR NOW! 9. The number 1 does not fit the definition of prime OR composite, and it needs to be crossed off first. 10. Remind the students that numbers that have 2 as a factor cannot be prime, and then model on the overhead: -Two (2) is highlighted because it is prime, but all multiples of 2 are NOT prime.
 10a. -Call on students to list aloud the factors of 4, 6, 8, and 10. Emphasize that since these numbers have more than two factors, they are NOT prime and must be crossed off. -Direct students to cross off all multiples of 2, lightly, in pencil. Model this on the overhead sheet by crossing off all multiples of 2. Count aloud to model this. -Remind the students that all even numbers are multiples of 2; the students can use that knowledge to help them cross off. 11. Model crossing off of all multiples of 3. Demonstrate that multiples are count-by numbers that can be found by crossing off every third number. Model this for the multiples of 3 at least halfway through the chart, counting aloud by threes. Let students complete crossing off multiples of threes.
 Accommodations for Special Education: -All work can be done with a partner. -Students may have notes about multiples, factors, etc. -Seat ESE students closer to teacher for more direct feedback at each step. -Use graphic examples to show factors, etc., such as geoboards or multiplication charts. Accommodations for ESOL: -Correlate terms such as multiples, factors, primes, etc. to the corresponding words in the students' home language(s). -Use graphic examples to show factors using diagrams, geoboards, etc. Extensions: Use the Weblinks below or other reference material to write a powergraph about Eratosthenes. Web Links Web supplement for Prime Real Estate This site shows a computer demonstration of the Sieve of Eratosthenes. Web supplement for Prime Real Estate This site contains biographical information on Eratosthenes. Web supplement for Prime Real Estate This site contains information about prime numbers and contains links to other sites.
Checking For Understanding:
 Assessments Evidence: Each student produces a 100 Number Chart (See Attached File) with the 25 primes highlighted. Criteria: All 25 primes between 1-100 are highlighted and correct.
 Wrap-up the lesson with a discussion of what prime numbers are, and introduce the term composite as numbers that are NOT prime, have more than 2 factors, etc.

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