6°LESSON 2: Prime and Composite Numbers

LESSON 2: Prime and Composite Numbers

What is a Prime Number?

• A number with only two factors,  $1$  and  the number itself. 

• It is called numeró primo  in Spanish.

•  $2$ is a prime. Why? Becasue  $2$  can only be divided by  $1$  and  $2$  

•  $3$ is a prime. Why?  Because $3$  can only be divided by  $1$  and  $3$  

•  $5$ is a prime . Why? Because $5$  can only be divided by  $1$  and  $5$  

Notes:

•  $0$  and  $1$  are not prime numbers. 

• The first prime number is  $2$   and it is even. All the other prime numbers are odd.

• There is an infinite number of primes. Mathematicians are often awarded huge amount of dollars in search of the largest prime.

Identify all the prime numbers in the figure. How many prime numbers are there?

Multiple Choice

 $13$ is a prime number.

• True

• False

Multiple Choice

 $15$  is a prime number.

• True

• False

Multiple Choice

 $21$  is a prime number.

• True

• False

Multiple Choice

 $27$  is a prime number.

• True

• False

Multiple Choice

 $31$  is a prime number.

• True

• False

Multiple Choice

 $1$  is a prime number.

• True

• False

What is a Composite Number?

• A number that is not a prime.

• It has more than  $2$  factors.

• It is called numeró compuesto in Spanish.

•  $4$  is a composite number. Why? Because it has the factors   $1,2,4$  

•  $12$  is a composite number. Why? Because it has the factors   $1,2,3,4,6,12$  

How many composite numbers are there in the figure? List them.

Multiple Choice

 $34$  

• Prime

• Composite

Multiple Choice

 $27$  

• Prime

• Composite

Multiple Choice

 $29$  

• Prime

• Composite

Multiple Choice

 $37$  

• Prime

• Composite

Multiple Choice

 $51$  

• Prime

• Composite

Multiple Choice

 $57$  

• Prime

• Composite

How to Find Prime Numbers?

Watch the video to find how to get the prime numbers using the Method of Eratosthenes.

Prime Factorization

• Prime factorization is a way of writing the number as a product of its prime factors.

• Example 1:   $4=2\cdot2$  

• Example 2:  $6\ =\ 2\cdot3$  

• Example 3:  $24\ =\ 2\cdot2\cdot2\cdot3$  

• Example 4:  $60\ =2\cdot2\cdot3\cdot5$  

How to Find Prime Factorization?

By the use of factor trees . See figure at the right for the prime factorization of 24 which is  $2\cdot2\cdot2\cdot3$  

Prime Factorization of  $48$  

 $48=2\cdot2\cdot2\cdot2\cdot3$  

Prime Factorization of  $42$  

 $42=2\cdot3\cdot7$  

Prime factorization of 16 using Factor Trees

Prime factorization of 30 using Factor Trees

Multiple Choice

Which is the prime factorization of   $20$  ?

•  $4\cdot5$  

•  $2\cdot10$  

•  $2\cdot2\cdot5$  

•  $1\cdot20$  

Multiple Choice

Which is the prime factorization of   $32$  ?

•  $2\cdot4\cdot4$  

•  $2\cdot2\cdot\cdot8$  

•  $4\cdot8$  

•  $2\cdot2\cdot2\cdot2\cdot2$  

Multiple Choice

Which is the prime factorization of   $50$  ?

•  $2\cdot5\cdot5$  

•  $5\cdot10$  

•  $2\cdot25$  

•  $25\cdot25$  

Activities in Lesson 2

• WORKSHEET 2. Upload photos of your work for grading.

• QUIZ 2. This is done in Socrative. Just click the link provided in Google Classroom.