Add and subtract fractions with unlike denominators
key notes:
1. Understanding Fractions with Unlike Denominators
- Fractions with different denominators cannot be directly added or subtracted.
- Example: 1/3+1/4 requires a common denominator before performing the operation.
2. Steps to Add or Subtract Fractions with Unlike Denominators
Step 1: Find the Least Common Denominator (LCD)
- Identify the least common multiple (LCM) of the denominators.
- The LCM becomes the common denominator.
Step 2: Adjust the Fractions
- Rewrite each fraction so they have the same denominator (LCD).
- Multiply both the numerator and denominator by the same number to create equivalent fractions.
Step 3: Perform the Operation
- Add or subtract the numerators while keeping the common denominator the same.
- Simplify the resulting fraction, if necessary.
3. Example of Addition
Learn with an example
Add.
1/4 + 4/12 =
Use the model to help you.
The model shows 1/4 + 4/12
Rename the fractions using a common denominator.
1/4 is the same size as 3/12
So, 1/4 + 4/12 is the same as 3/12 + 4/12
Now add.
1/4 + 4/12 = 7/12
Subtract.
7/10 – 2/5 =
Use the model to help you.
The model shows
7/10 – 2/5 .
Rename the fractions using a common denominator.
2/5 is the same size as 4/10
So, 7/10 – 2/5 is the same as 7/10 – 4/10
Now subtract.
7/10 – 2/5 = 3/10
Subtract.
5/12 – 2/6
Use the model to help you.
The model shows
5/12 – 2/6 .
Rename the fractions using a common denominator.
2/6 is the same size as 4/12 ,
So, 5/12 – 2/6 is the same as 5/12 – 4/12 .
Now subtract.
5/12 – 2/6 = 1/12
let’s practice:
