Adding and Subtracting Mixed Numbers

Why can't we just add the numerators and denominators if we need to add two fractions with different denominators?

• Because you need to simplify them first

• You can

• Because the size of the pieces is different

• Because they are improper fractions

Addition:
Find Lowest Common Denominator & solve
1    1/3   +    4    1/4 =

• 5    7/12
• 5    2/24
• 5    2/12
• 5    7/24

Addition:
Find Lowest Common Denominator & solve
8     4/5    +    9    1/10  =

• 18   5/15
• 17   5/10
• 17   9/20
• 17   9/10

 $2\frac{9}{10}\ +6\ \frac{1}{3}=$  

•  $9\ \frac{7}{30}$  

•  $5\ \frac{4}{9}$  

•  $6\ \frac{1}{4}$ 

•  $4\ \frac{1}{2}$  

Subtraction:
Find Lowest Common Denominator & solve
8    6/9    -    3    2/5  =

• 6
• 4
• 5   12/45
• 5   4/60

 $6\ \frac{2}{4\ }-2\ \frac{2}{5}=$  
Reduce if needed.

•  $5\ \frac{2}{7}$  

•  $4\ \frac{2}{20}$  

•  $6\ \frac{1}{2}$  

•  $4\ \frac{1}{10}$  

 $12\ \frac{1}{4}\ -\ 5\ \frac{2}{3}\ =$  

Answer in simplest form. 

•  $7\ \frac{7}{12}$  

•  $6\ \frac{7}{12}$  

•  $7\ \frac{1}{2}$  

•  $7\ \frac{3}{7}$  

 Subtraction:
Find Lowest Common Denominator & solve 
8    5/7    -    7    2/3 = 

• 1    3/4
• 1   1/21
• 1     1/24 
• 1    3/24

 $21\ \frac{7}{12}\ -11\ \frac{5}{6}\ =$  

Answer in simplest form. 

•  $10\ \frac{2}{6}$  

•  $10\ \frac{2}{12}$  

•  $9\ \frac{7}{12}$  

•  $9\ \frac{3}{4}$  

6½ - 2⅔

• 4  1/6
• 3  5/6
• 4  1/2
• 3  1/2