1. HW: Index Numbers 3. Fill the blanks: 1. Fill the blanks:
2. Find the value of: a) a) e) b) b) f) c) d) c) g) e) d) h)

2. Grow these factor bugs, their legs7 5 19 17 23

3. What’s special about these factor bugs?
They only have 2 legs! They are prime bugs! Numbers which have only two factors - 1 and itself are
PRIME NUMBERS

4. L.O. To be able to identify prime numbers5 37 2 23 11
L.O. To be able to identify prime numbers
By the end of the lesson, we will be able to:
understand what a prime number is
define a prime number
identify a prime number at least up to 100
understand how divisibility tests help us identify prime numbers 41 3 19 17 7 43 13 29 31 47

5. PRIME NUMBER SEARCH 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99
100 ## ## ## ## ## ## ## ## ## ##
TASK
NOTE THAT THEY END IN 1,3,7,9 !!!
Challenge
Why did you not have to cross out multiples of 4,6,8 and 9?
1) Cross out the number 1.
2) Do NOT cross out 2. Cross out all the multiples of 2.
3) Do NOT cross out 3. Cross out all the multiples of 3.
4) Do NOT cross out 5. Cross out all the multiples of 5.
5) Do NOT cross out 7. Cross out all the multiples of 7.
Did you manage to find all 25 prime numbers between 1 and 100?

6. Can you identify prime numbers?
The prime numbers up to 50 are:
2, 3, ____, 7, ____, 13, ____, ____, ____, 29, 31, ____, 41, ____, _____ 5 11 17 19 23 37 43 47
If you can think of at least one other pair of factors that make the number, it’s not prime!

7. Can you identify prime numbers?
What is the only prime number between 90 and 100 97
Why did I not even consider 92,94,95,96 ?? 91 93 97 99
3 x 33
7 x 13
3 x 31

8. Can you identify prime numbers?
How many prime numbers are there between 50 and 80? 7
Divisible by 3, Even numbers – divisible by 2 , ending in 0 or 5 divisible by 5, both numbers the same divisible by 11 51 53 57 59 61 67 71 73 79
3 x 17
3 x 19

9. Can you identify prime numbers?
What is the first prime number after 100?
101
Divisible by 3, Even numbers – divisible by 2 , ending in 0 or 5 divisible by 5, both numbers the same divisible by 11

10. Can you identify prime numbers?
Which is the ONLY even prime number? 2
Divisible by 3, Even numbers – divisible by 2 , ending in 0 or 5 divisible by 5, both numbers the same divisible by 11

11. Can you identify prime numbers?
Is 1 a prime number?
No, because it has only 1 factor
Divisible by 3, Even numbers – divisible by 2 , ending in 0 or 5 divisible by 5, both numbers the same divisible by 11

12. Well, CAN YOU?

13. To check if prime – check divisibility
Is the last number even? DIVISIBLE BY 2
NOT PRIME
Is the last number 0 or 5 ? DIVISIBLE BY 5
Is the sum of the numbers divisible by 3? DIVISIBLE BY 3
Is is a double number? DIVISIBLE BY 11