We finally got back to prime and composite numbers.

: Math Makes Sense__Today’s Lesson__- Chapter 2, Lesson 5 - Prime and Composite Numbers (Pages 45-47)
__Learning Goals:__- A number with exactly two factors, 1 and itself, is a prime number.
- A number with more than two factors is a composite number.
- The number 1 is neither prime nor composite.
: Practice Questions 1-11__Classwork__- Hand in #5 & 8 – Show your work
: Pages 20-21__Homework Book__

An important concept that we talked about today in class was that you could eliminate possibilities in order to come up with a correct answer. For example if I want to know which of the numbers between 40 and 50 are prime, I could list all of the the numbers, and then explain why some aren’t prime (i.e. are composite) and the numbers that remain are prime.

- Possible prime numbers: 40 41 42 43 44 45 46 47 48 49 50
- 40, 42, 44, 46, 48, and 50 are all even numbers that can be divided by two so they aren’t prime.
- 41, 43, 45, 47, 49 remain
- 45 is a multiple of 5 (5 x 9) so it isn’t prime.
- 41, 43, 47, 49 remain
- 49 is a multiple of 7 (7 x7) so it isn’t prime.
- 41, 43, 47 remain
- Now I only have three numbers to test using division. I will test them to see if they can be divided by any of the low prime numbers that I haven’t already dealt with.
- None of these can be divided by 2, 3, 5, 7 or 11 so they must be prime!
- 41, 43, 47 are prime numbers.