Friday, July 18, 2014

Adding and Subtracting Fractions with Unlike Denominators

Preview

Addition and subtraction of fractions with unlike denominators is just the same thing as simple addition and subtraction of fractions so let's take the two fractions 5/7 and 3/8 and let's start by first putting these fractions in vertical form:

    5
    7
+
    3
    8

And now we have to find the LCM of the two denominators 7 and 8 and rename the fractions like this:

    5
    7        7,14,21,28,35,42,49,56
+       =  
    3        8,16,24,32,40,48,56,64
    8

   40
   56
+       
   21
   56
So now all we have to do is add the numerators and put the denominator as it is in the fraction like this:

   40
   56      61
+       =  56  
   21
   56
So now we have a improper fraction as our answer so you can either leave as it is or if you want make it an improper fraction.

Now let's take the fractions 6/12 and 2/6 and let's subtract by first putting them in vertical form:
   
   12
-      
    2
    6
Next you have to find the LCM of the two denominators 12 and 6 and rename the fractions like this:
    6 
   12      12,24,36,48,60
-       = 
    2         6,12,18,24,30
    6

  6
 12    
-      
   4
  12
Now you have to simply subtract the numerators and bring the denominator as it is like this:
  12
  24       4        1
-       =  24  =  6
   8 
  24
So our final answer is 4/24 or the simplified term 1/6.
Now try some of these and make sure to watch the video on YouTube.


Sheet 1 Adding and Subtracting Fractions with Unlike Denominators







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