1. Lesson #7
LCM and GCF

2. Factor trees

3. Greatest common divisor (GCD)
To find a common divisor we need to list all the numbers that the number is divisible by.
Pick the greatest that is common.
Ex. What is the GDC of 20 and 10
20: 1,2,4,5,10,20
10: 1,2,5,10

4. Lowest Common Multiple (LCM)
To find a common multiple between 2 numbers we need to list the all the numbers that are multiples.
Pick the lowest that is common
Ex. What is the LCM of 3 and 5?
3:3,6,9,12,15,18,21
5:5,10,15,20,25,30

5. MULTIPLES (first 4)
FACTORS 24 10 35
Multiples you must multiply ( x ). Divisors or Factors you must divide (÷).

6. Examples:
Find the LCM of:
12 and 24
12:
24:
GCD for 12 and 24 =

7. Find GCD for 27, 36, and 54
27:
36:
54:
GCD for 27, 36, and 54 =

8. When do we need GCD?
Making teams or dividing more than one thing equally
Simplify fractions

9. Example
Mr. Beaudoin wants to make equal teams with all the same number of boys and girls. There are 32 boys and 24 girls. What is the maximum number of teams and how many boys and girls will there be in each?

10. When do I need LCM Planning a common meeting time.
Seeing when 2 buses or trains pass at the same time.

11. Example: I have meetings with middle school every 15 days and with the Pre work program every 30 days. How many days will pass before I see both on the same day?