Adding Fractions 1. Adding Fractions with Common Denominators Add the Numerators. Keep the Denominators the same. 2. Practice time 3. Reduce or simplify if necessary… 4. Adding Fractions with Unlike Denominators 5.Find a common denominator using LCM. Multiply numerator and denominator by LCM. Add the converted fractions. 6. Least Common Multiple 7. We need to create fractions with like denominators in order to add these fractions. This is where we need LCM (Least Common Multiples) 8. The first common multiple is the Least Common Multiple This will become the new denominators in order to create like denominators to add fractions. 9. Adding Fractions with Unlike Denominators Multiples of 7: 7, 14, 21, 28 Multiples of 4: 4, 8, 12, 16, 20, 24, 28 10. Practice time Common Multiples for these numbers: 6: 5: What is the LCM? 11. 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?

2. 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
=

4. +
2
9
=
9
5
9
16
+
4
16
=

5. 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?

6. +
2
9
=
9
4
+
3
12
=
12
6

7. +
2
15
=
15
7
+
1
16
=
16
1

8. 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?

10. +
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)

11. 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)

12. 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

13. 3
7
12
28
=
3
4 =
21
28
X 4
X 4
X 7
X 7
3 3
7 4
+
12 21
28 28
+
START
READY
TO ADD

14. Common Multiples for these numbers:
6:
12:
What is the LCM?

15. Common Multiples for these numbers:
8:
12:
What is the LCM?

16. Common Multiples for these numbers:
9:
12:
What is the LCM?

17. Common Multiples for these numbers:
4:
12:
What is the LCM?

18. Common Multiples for these numbers:
3:
5:
What is the LCM?

19. Common Multiples for these numbers:
7:
16:
What is the LCM?

20. Common Multiples for these numbers:
6:
5:
What is the LCM?

21. +
2
3
=
9
4
What is the LCM that you need for a
common denominator?

22. +
4
9
=
12
5
What is the LCM that you need for a
common denominator?

23. +
4
7
=
9
5
What is the LCM that you need for a
common denominator?

24. +
2
3
=
6
5
What is the LCM that you need for a
common denominator?

25. +
4
9
=
2
1
What is the LCM that you need for a
common denominator?

26. 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?