SME
Grade 6 Math · The Number System
Greatest common factor and least common multiple
Use this for “What is the greatest common factor of 12 and 18?”
Diagram
Common factors of 12 and 18: 1, 2, 3, 6.
The greatest is 6.
This is an example. Type your own values to start a new problem.
The
greatest
common
factor
of
a
and
b
is
g
Formulas
greatest common factor of 12 and 18: 6
The greatest number that divides both = greatest common factor
Assumptions
•
A common factor divides both numbers with nothing left over.
•
1 is a common factor of any two numbers.
•
Whole numbers from 1 to 100.
Step-by-step
WE KNOW
First number: 12
Second number: 18
FIND
greatest common factor
Step 1 · Find greatest common factor
greatest common factor of 12 and 18: ?
The greatest number that divides both = greatest common factor
List the factors of each number. Find the ones in both lists; take the greatest.
Factors of 12: 1, 2, 3, 4, 6, 12
Factors of 18: 1, 2, 3, 6, 9, 18
Common factors: 1, 2, 3, 6
Greatest common factor = 6
Check
Put the numbers back in. Both sides should match.
greatest common factor of 12 and 18: 6 ✓
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