Fractions
• Like denominators- just add the numerator.
• Example: 2/5 + 2/5= 4/5
Like Denominators
• Guided Practice:
12/ 15 + 2/15
Try on your own: 6/23 + 7/23
Unlike denominators
• Step 1: find the LCM of the denominators Step 2: multiply both the top and the bottom by that number
• Step 3: Make sure it doesn’t need to be simplified
• Look at the next slide for example
We need a common denominator to add
these fractions.
x 2
x 2
X 7
x 7 7
6
7 + 6 = 13
13
We need a common denominator to add
these fractions.
x 7
x 7
X 5
x 5 15
7
15 + 7 = 22
22
We need a common denominator to add
these fractions.
7, 14, 21, 28, 35, 42, 49, 56, 63
8, 16, 24, 32, 40, 48, 56, 64, 72
x 7
x 7
x 8
x 8 32
2132 + 21 = 53
53
We need a common denominator to add
these fractions.
3, 6, 9, 12, 15, 18, 21, 24, 27
5, 10, 15, 20, 25, 30, 35, 40, 45
X 3
x 5
x 5
x 3 9
10
9 + 10 = 19
19
We need a common denominator to add
these fractions.
3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33
11, 22, 33, 44, 55, 66, 77…
x 11
x 11
X 3
x 3 15
2215 + 22 = 37
37
We need a common denominator to add
these fractions.
x 11
x 11
X 6
x 6 18
11
29
18 + 11 = 29
We need a common denominator to add
these fractions.
We need a common denominator to add
these fractions.
x 5
x 5
x9
x 936
3536 + 35 = 71
71
36 + 35 = 71
Try These
A
F
EB
C
D
Try These
A
F
EB
C
D1727
1920
109
4128
2621
1312
Subtracting Fractions
• The steps are just like adding fractions, but instead of adding the numerators, you subtract the numerators.
We need a common denominator to
subtract a fraction from another.
x 5
x 5
x 11
x 11
4
15 - 11 = 4
15
11
x 1
x 1
x 5
x 5
2
5 – 3 = 2
5
3