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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