adding fractions
Post on 22-May-2015
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Adding Fractions with Common Denominators
1. Add the Numerators.
2. Keep the Denominators the same.
3 5+
11 11
=8
11
3 5+
11 11=
+2
9=
9
5
9
16+
4
16=
Reduce or simplify if necessary…
2
15+
3
15=
5
15
5
15÷
5
5=
1
3
What does it mean to reduce
or simplify?
+2
9=
9
4
+3
12=
12
6
+2
15=
15
7
+1
16=
16
1
Adding Fractions with Unlike Denominators
1. Find a common denominator using LCM.
2. Multiply numerator and denominator by LCM.
3. Add the converted fractions.
What is an LCM?
+2
3
=
6
5
We need to create fractions with like denominators in order to add these fractions. This is where we need LCM (Least Common Multiples)
3: 3, 6, 9, 12, 15, 18
6: 6, 12, 18
•The first common multiple is the Least Common Multiple
• This will become the new denominators in order to create like denominators to add fractions.
•List the multiples for each of the factors (denominators)
Adding Fractions with Unlike Denominators
3
7+
3
4=
Multiples of 7:
Multiples of 4:
7, 14, 21, 28
4, 8, 12, 16, 20, 24, 28
3
7
1228
=
3
4 =
21
28
X 4
X 4
X 7
X 7
3 3
7 4 +
12 21
28 28 +
START
READY TO ADD
Common Multiples for these numbers:
6:
12: What is the LCM?
Common Multiples for these numbers:
8:
12: What is the LCM?
Common Multiples for these numbers:
9:
12: What is the LCM?
Common Multiples for these numbers:
4:
12: What is the LCM?
Common Multiples for these numbers:
3:
5: What is the LCM?
Common Multiples for these numbers:
7:
16: What is the LCM?
Common Multiples for these numbers:
6:
5: What is the LCM?
+2
3=
9
4
What is the LCM that you need for a common denominator?
+4
9=
12
5
What is the LCM that you need for a common denominator?
+4
7=
9
5
What is the LCM that you need for a common denominator?
+2
3=
6
5
What is the LCM that you need for a common denominator?
+4
9=
2
1
What is the LCM that you need for a common denominator?
REVIEW
• In order to add fractions, what must you have?
• Explain a simplified fraction
• What is an LCM?
• What are LCMs used for?
• Why is it important to be able to find an LCM?
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