Adding and Subtracting Fractions with the Same Denominators.

1
4
2
4
+
Read this sum out loud.
Do these fractions have the same
denominator?

1
4
2
4
+
The fractions have the same
denominator
quarters

1
4
2
4
+ =
?
?
How do we add these two fractions?

1
4
2
4
+ =
?
4
Because both denominators are the same,
we do not change it, so it must be quarters.

1
4
2
4
+
=
3
4
Now we add the numerators. 1 + 2 = 3.

1
4
2
4
+ =
3
4
Here is our answer!

1
4
2
4
+
One quarter plus two quarters
equals three quarters.
quarters
3
4
=

3
8
2
8
+
denominator?

3
8
2
8
+
denominator
eighths

3
8
2
8
+ =
?
?
How do we add these two fractions?

3
8
2
8
+ =
?
8
we do not change it, so it must be eighths.

3
8
2
8
+
=
5
8
Now we add the numerators. 3 + 2 = 5.

3
8
2
8
+ =
5
8
Here is our answer!

3
8
2
8
+
Three eighths plus two eighths
equals five eighths.
eighths
5
8
=

4
7
2
7
+
Four sevenths plus two sevenths
equals six fourteenths.
6
14
Is this correct ?
Who can explain why it’s wrong ?
=

4
7
2
7
+
It’s wrong because both of the
denominators are sevenths.
6
14
So the answer must be
in sevenths because we
don‘t change the denominator.

4
7
2
7
+ =
?
?
Who can tell me the answer?
Remember we don’t change the denominator!

4
7
2
7
=
Four sevenths plus two sevenths
equals six sevenths.
6
7
The answer must be in
sevenths because the denominator
stays the same!
+

Now it’s time for you to try some.
You can discuss these with a friend.
Thinking time starts now !
3
6
1
6
2
9
5
9
4
7
1
7
4
8
3
8
?
?
?
?
?
?
?
?
+
+
+
+
=
=
=
=

The answers.
How did you do?
3
6
1
6
2
9
5
9
4
7
1
7
4
8
3
8
4
6
5
7
7
9
7
8
+
+
+
+
=
=
=
=

4
5
2
5
-
denominator?

4
5
2
5
-
denominator
fifths

4
5
2
5
- =
?
?
How do we subtract one fraction from another?

4
5
2
5
- =
?
5
we do not change it, so it must be fifths.

4
5
2
5
-
=
2
5
Now we subtract the second numerator
from the first numerator. 4 – 2 = 2.

4
5
2
5
- =
2
5
Here is our answer!

4
5
2
5
-
Four fifths minus two fifths
equals two fifths.
fifths
2
5
=

6
7
5
7
-
denominator?

6
7
5
7
-
denominator
sevenths

6
7
5
7
- =
?
?
How do we subtract one fraction from another?

6
7
5
7
- =
?
7
we do not change it, so it must be sevenths.

6
7
5
7
-
=
1
7
Now we subtract the second numerator
from the first numerator. 6 – 5 = 1.

6
7
5
7
- =
1
7
Here is our answer!

6
7
5
7
-
Six sevenths minus five sevenths
equals one seventh.
sevenths
1
7
=

Now it’s time for you to try some.
You can discuss these with a friend.
Thinking time starts now !
3
8
1
8
2
4
1
4
5
9
2
9
6
6
2
6
?
?
?
?
?
?
?
?
-
-
-
-
=
=
=
=

3
8
1
8
2
4
1
4
5
9
2
9
6
6
2
6
2
8
3
9
1
4
4
6
-
-
-
-
=
=
=
=
The answers.
How did you do?

Adding and Subtracting Fractions with the Same Denominators.

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