Unformatted text preview: Fraction X
Fraction X
Adding Unlike Denominators
By Monica Yuskaitis Reminder
Reminder
Be sure to do Fractions IX before continuing with this lesson. Common Multiple
Common Multiple
A number that is a multiple of two or more numbers. Some multiples of 3 & 6
6, 12, 18, 24, 30, 36, 42 Least Common Multiple
Least Common Multiple The smallest common multiple of a set of two or more numbers. 5 = 5, 10, 15, 20, 25, 30
6 = 6, 12, 18, 24, 30, 36 Shortcut for Finding the Least Shortcut for Finding the Least Common Denominator or Least Common Multiple
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
3
1
+9 3 will divide evenly into 9,
so 9 is your LCD or LCM. To Add or Subtract Fractions To Add or Subtract Fractions With Unlike Denominators Find the multiples of each denominator. 1
5 = 5, 10, 15, 20, 25, 30
1
+10 = 10, 20, 30, 40, 50 To Add or Subtract Fractions To Add or Subtract Fractions With Unlike Denominators Compare the lists of multiples. Circle the common multiples between the two lists. 1
5 = 5, 10, 15, 20, 25, 30
1
+10 = 10, 20, 30, 40, 50 To Add or Subtract Fractions 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 To Add or Subtract Fractions 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 To Add or Subtract Fractions To Add or Subtract Fractions With Unlike Denominators Rewrite the fractions using the least common denominator or least common multiple. 1
5
1
+10 10
10 To Add or Subtract Fractions To Add or Subtract Fractions With Unlike Denominators Find the equivalent fractions for 1/5 & 1/10 with 10 as the denominator.
You know that 1/10
1
is equal to 1/10 so
5
10
Put a 1 over the
1
1
Bottom 10.
+10
10 To Add or Subtract Fractions To Add or Subtract Fractions With Unlike Denominators Find the equivalent fractions for 1/5 & 1/10 with 10 as the denominator.
To find the top
1
number, ask yourself
5
10
what do you multiply
1
1
the 5 by to get 10.
+10
10 To Add or Subtract Fractions To Add or Subtract Fractions With Unlike Denominators Find the equivalent fractions for 1/5 & 1/10 with 10 as the denominator.
That’s right 2. Since
you are looking for
1x 2 =
equivalent fraction
5 x 2 = 10 theyou know the top
1
1 number must also be
+10
10
multiplied by 2. To Add or Subtract Fractions To Add or Subtract Fractions With Unlike Denominators Find the equivalent fractions for 1/5 & 1/10 with 10 as the denominator.
1 x 2 = 2 To find the top2number
just multiply x 1 to
5 x 2 = 10 get your equivalent
1
1
fraction. +10 10 To Add or Subtract Fractions To Add or Subtract Fractions With Unlike Denominators Now just add the numerators. 1x 2 = 2
5 x 2 = 10
1
1
+10
10
3
10 Remember when
adding fractions
you never add the
denominators. Add these Fractions
Add these Fractions 1
2
1
+8 8
8 Use the short
cut to find the
Least Common
Denominator
(LCD). Add these Fractions
Add these Fractions 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. Add these Fractions
Add these Fractions 1x 4 =
2x 4 = 8
1x 1 =
+ 8 x 1 =8 Since you are
writing equivalent
fractions, now
multiply the top
numbers by the
same number you
did in the
bottom. Add these Fractions
Add these Fractions 1x 4 = 4
2x 4 = 8
1x 1 =1
+ 8x 1 =8 Now multiply
across. Add these Fractions
Add these Fractions 1x 4 = 4
2x 4 = 8
1x 1 =1
+ 8x 1 =8
5
8 Add your
new
numerators. Add these Fractions
Add these Fractions 2
5
1
+3 15
15 Find the
common
Multiples for
5 and 3. Write
This number
As your new
denominator. Add these Fractions
Add these Fractions 2
5 x 3 = 15
1
+ 3 x 5 =15 Ask yourself
what you
multiply the
bottom number
by to get 15. Add these Fractions
Add these Fractions 2x 3 =
5 x 3 = 15
1x 5 =
+ 3 x 5 =15 Multiply the
top number
by the same
number you
did in the
bottom. Add these Fractions
Add these Fractions 2x 3 = 6
5 x 3 = 15
1x 5 =5
+ 3 x 5 =15 Multiply
across. Add these Fractions
Add these Fractions 2x 3 = 6
5 x 3 = 15
1x 5 =5
+ 3 x 5 =15
11
15 Now add
your new
numerators. Add these Fractions
Add these Fractions 1x 2 = 2
6 x 2 = 12
1x 3 =3
+ 4 x 3 =12
5
12 Add these Fractions
Add these Fractions 5 x 4 = 20
6 x 4 = 24
1x 3 =3
+ 8 x 3 =24
23
24 Add these Fractions
Add these Fractions 2x 3 = 6
3x 3 = 9
1x 1 =1
+ 9x 1 =9
7
9 Add these Fractions
Add these Fractions 4 x 3 = 12
5 x 3 = 15
2 x 5 = 10
+ 3 x 5 = 15
22
15 Simplify Your Answer
Simplify Your Answer 22
15 7
1 15
15) 22
15
7 ...
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 Fall '11
 BrotherRaymond
 Fractions, Elementary arithmetic, Greatest common divisor

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