Download Add & Subtract Fractions

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Parts of a Fraction
3
4
= the number of parts
= the total number of parts
that equal a whole
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Parts of a Fraction
3 = numerator
4 = denominator
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A Common Multiple is a
number that is a multiple of
two or more numbers.
Some multiples of 3 & 6
6, 12, 18, 24, 30, 36, 42
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The LCM is the smallest multiple
that two numbers have in
common.
5 = 5, 10, 15, 20, 25, 30
6 = 6, 12, 18, 24, 30, 36
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To Add or Subtract Fractions
With Unlike Denominators
List the multiples of each
denominator to find the LCM.
1
5 = 5, 10, 15, 20, 25, 30
1
+ 10 = 10, 20, 30, 40, 50
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To Add or Subtract Fractions
With Unlike Denominators
Compare your lists. Which multiples
do 5 and 10 have in common?
1
5 = 5, 10, 15, 20, 25, 30
1
+ 10 = 10, 20, 30, 40, 50
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To Add or Subtract Fractions
With Unlike Denominators
Use the lowest common
multiple as the denominator.
1
5 = 5, 10, 15, 20, 25, 30
1
+ 10 = 10, 20, 30, 40, 50
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To Add or Subtract Fractions
With Unlike Denominators
This number is also called the
least common denominator.
1
5 = 5, 10, 15, 20, 25, 30
1
+ 10 = 10, 20, 30, 40, 50
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SHORTCUT: Check to see if the smaller
denominator divides evenly into the larger
denominator. If it does, use the larger
denominator for your LCD or LCM.
1
5
1
+ 10
5 will divide evenly into 10,
so 10 is your denominator.
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Rewrite the fractions using the least
common denominator or least
common multiple.
1
5
1
+10
10
10
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Find the equivalent fractions for 1/5
& 1/10 with 10 as the denominator.
1
5
1
+10
10
1
10
You know that 1/10
is equal to 1/10 so
Put a 1 over the
Denominator of 10.
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Find the equivalent fractions for 1/5
& 1/10 with 10 as the denominator.
1
5
1
+10
10
1
10
To find the top
number, ask yourself
what do you multiply
the 5 by to get 10.
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Find the equivalent fractions for 1/5
& 1/10 with 10 as the denominator.
2
1 x2=
5 x 2 10
1
1
+10
10
Since you are looking
for the equivalent
fraction you know the
numerator must also be
multiplied by 2.
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Now just add the numerators.
2
1 x2=
5 x 2 10
1
1
+10
10
Remember when
adding fractions
you never add the
denominators.
3
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Identity Property states that any number
multiplied by one equals itself
n 1  n
2
3
2
4

2
6
This is useful to know so you can find a
common denominator for adding and subtracting
fractions.
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1
2
1
+8
8
8
Use the short
cut to find the
Least Common
Denominator
(LCD).
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1
2x 4 = 8
1
+ 8 x 1 =8
Now find the
equivalent
fractions for
1/2 & 1/8.
Ask what do you multiply 2 by to get 8
and what do you multiply 8 by to get 8.
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1x 4 = 4
2x 4 = 8
1
+ 8 x 1 =8
Since you are
writing equivalent
fractions, now
multiply the
numerator by the
same number you
did on the
denominator.
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1x 4 = 4
2x 4 = 8
1 x 1 =1
+ 8 x 1 =8
Since you are
writing equivalent
fractions, now
multiply the
numerator by the
same number you
did on the
denominator.
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1x 4 = 4
2x 4 = 8
1 x 1 =1
+ 8 x 1 =8
5
8
Now add
numerators.
The denominator
stays the same.
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2
5
1
+3
15
15
Find the least
least common
multiple for 5
and 3. Write it as
your denominator
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2
5 x 3 = 15
1
+ 3 x 5 =15
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Ask yourself
what do you
multiply the
denominator
by to get 15.
2x 3 = 6
5 x 3 = 15
1
+ 3 x 5 =15
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Multiply the
numerator
by the same
number you
did in the
denominator
2x 3 = 6
5 x 3 = 15
1x 5 =5
+ 3 x 5 =15
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Multiply the
numerator
by the same
number you
did in the
denominator.
2x 3 = 6
5 x 3 = 15
1x 5 =5
+ 3 x 5 =15
11
15
Add your
numerators. The
denominator
stays the
same.
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1x 2 = 2
6 x 2 = 12
1x 3 =3
+ 4 x 3 =12
5
12
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4 x 3 = 12
5 x 3 = 15
2 x 5 = 10
+ 3 x 5 = 15
22
15
ALWAYS SIMPLIFY
YOUR ANSWER
IF YOUR
ANSWER IS AN
IMPROPER
FRACTION!
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22
15
1
7
15
15) 22
15
7
ALWAYS SIMPLIFY YOUR ANSWER
IF YOUR ANSWER IS AN
IMPROPER FRACTION!
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5 x 4 = 20
6 x 4 = 24
1x 3 =3
- 8 x 3 =24
17
24
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2x 3 = 6
3x 3 = 9
1x 1 =1
- 9x 1 =9
5
9
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2x 2 = 4
4x 2 = 8
2x 1 =2
+ 8x 1 =8
6
8
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=
3
4
4x 3 =
5x 3 =
2x5=
-3 x5=
12
15
10
15
2
15
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REMEMBER:
To Always Show Your Work
and The Giant One!
Take out your study guide!!!
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#11
4x3=
5x3=
2x5=
+3 x5=
1
15) 22
15
Add Fractions
12
15
10
15
7 22
15 15
1) Find a common
denominator.
2) Add the numerators.
3) Keep the common
denominator the same.
4) Simplify or reduce.
Change improper
fractions to mixed #s.
7
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#12
Subtract Fractions
5x4=
6x4=
1 x3=
x
3
=
8
-
20
24
3
24
17
24
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Always SHOW
YOUR WORK!
This includes the
Giant One.