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FRACTIONS WITH UNLIKE DENOMINATORS
ADDING AND SUBTRACTING

We can use fraction bars to add fractions with unlike denominators.  We put the fractions into the same denominator and then add. 

To add fractions with different denominators, we find the LCD, least common denominator.  Once we find the LCD, we express each fraction into the same denominator and then all that’s left is to add the numerators.

We will also take a look at subtracting fractions using fraction bars. 

To subtract fractions with different denominators, we find the LCD, least common denominator.  We then express each fraction into the same denominator and all that’s left is to subtract the numerators. 

Estimating fractions helps to determine an approximate answer.  We can use it as a quick check just to make sure our answer is reasonable.  We will look at rounding to the nearest half and apply it to solving a word problem where the answer required is just an estimate.

Write fraction answers using the form in these examples.
Example 1:  two-thirds is written as 2/3.
Example 2:  five and three fourths is written as 5 3/4.

Fraction Bars

 

Look over these fraction strips.  Each strip represents 1 whole. 

 

1 = 2 halves, 3 thirds, 4 fourths, 5 fifths, 6 sixths, and so on.

 

Thus, 1 = 2/2 = 3/3 = 4/4 = 5/5 = 6/6 and so on…


Adding Fractions with Unlike Denominators Using Fraction Bars

 

Study the two addition problems below.  To add fractions with unlike denominators, express the fractions into equivalent fractions with the same denominator.

Example 1:



Example 2:

Adding Fractions with Unlike Denominators


Subtracting Fractions Using Fraction Bars

Subtracting Fractions

Example 1:  Find 11/12 – 5/12.  Simplify, if necessary.


Thus, 11/12 – 5/12 = 1/2.

 

 

Example 2:  Find 7/8 – 5/6.  Simplify, if necessary.

 


 Completion to 1
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Rounding and Estimating with Fractions

 

Rounding

 

Round each fraction to the nearest half.




Estimating

 

Use estimation to solve this word problem.

 

Donnie's dad is planning to fence in a rectangular area of the yard for his new puppy.  The area will be 40 2/3 foot long and 30 1/3 foot wide.  To the nearest half foot, approximately how much fencing must be purchased?

 

Since 2/3 is more than 1/2, round 40 2/3 to 41. 

Since 1/3 is less than 1/2, round to 30 1/3 to 30.

 

Approximately 142 feet of fence is needed.  (41 + 41 + 30 + 30)
 Estimating Fractions




Below are additional educational resources and activities for this unit.
 
Click on the icon to find and practice topics for this unit.
 
Unit 8 Fraction Bars Worksheet
 
Unit 8 Adding Fractions Worksheet
 
Unit 8 Subtracting Fractions Worksheet