We can find a multiple
by multiplying the numbers
together, but to find the
Least Common Multiple we
have to get rid of any
factors that the numbers
have in common.
What’s the LCM
of 4 and 6?
Multiples of 4:
4, 8, 12, 16, 20, 24 ….
Multiples of 6:
6, 12, 18, 24, 30, 36 …
How can we find the LCM
without listing multiples? How
can we “get rid of” the factor(s)
that 4 and 6 have in common?
Use Prime
Factors
Prime factors of 4:
Prime factors of 6:
2X2
2X3
What do they have in common?
Get rid of the second one.
Now multiply what you have left
2 X 2 X 3 = 12
Here’s how this works:
Find the Least Common Multiple of
18 and 27.
18
Find prime
factors.
2
2
27
3
9
3 3
3
9
3 3
18 = 2 X 3 X 3
27 = 3 X 3 X 3
Find common factors.
Get rid of the extras of each
repeated factor.
Multiply what’s left -
2X3X3X3=
54
54 is the
Least
Common
Multiple
of 18 and 27.