2. * Remember from the previous section, that in
order to add or subtract fractions, they need to
be the same size pieces of the whole
* This section will demonstrate how to
add/subtract fractions that don’t have a
common denominator (or aren’t same size
pieces)
*
7. *Notice that we need the WHOLE to be
separated into the same number of same area
pieces.
*This allows us to have a common denominator
*We then use the equivalent fraction that has
that same denominator
(remember talking about
equivalent fractions earlier?)
*So instead of drawing a picture each time, we
can just use equivalent fractions to cut the
whole into the same number of pieces
COMMON DENOMINATOR
8. *
*The Least Common Denominator(LCD) is the smallest
number that both denominators will divide into
*The smallest number that you can cut both
rectangles into so that the pieces are all the same
size
*We will be using the Least Common Multiple
(LCM) of the given denominators to determine
the LCD
*There are a couple of ways to determine the LCM, but
I’m only going to show one way here (google/youtube it
if you want to know the other way)
9. *
1.
2.
list the multiples of each number
3.
That number is the LCM
Locate the smallest number that is a multiple of both
numbers
Example: Determine the LCM of 6 & 9
Multiples of 6: 6, 12, 18, 24, 30, 36, …
Multiples of 9: 9, 18, 27, 36, 45, …
The LCM of 6 & 9 is
18
10. *
Example: Determine the LCM of 3 & 7
Multiples of 3: 3, 6, 9, 12, 15, 18, 21, 24, 27, …
Multiples of 7: 7, 14, 21, 28, 35, …
The LCM of 3 & 7 is
21
Example: Determine the LCM of 12 & 15
Multiples of 12: 12, 24, 36, 48, 60, 72, 84, …
Multiples of 15: 15, 30, 45, 60, 75, 90, …
The LCM of 12 & 15 is
60
11. *Now let’s get some practice
determining the LCM by playing a
quick game, then we’ll continue
with adding & subtracting
fractions with uncommon
denominators!
