Upload
nicholas-manning
View
240
Download
0
Embed Size (px)
Citation preview
Adding and Subtracting Fractions and Mixed
Numbers
Agenda
• Finding the Least Common Multiple• Adding Fractions with Unlike Denominators• Adding Mixed Numbers• Short Quiz on Quia
LCM?
• When we add or subtract fractions, the denominator has to be the same, so the size of the parts we are adding or taking away is the same.
• To get the denominators to be the same, we have to find their lowest common multiple and use that as the denominator.
Let’s Practice Finding the Least Common Multiple!
• LCM = Least Common Multiple.
• What are the multiples of 4?• 4, 8, 12, 16, 20, 24, 28, 32…
• What are the multiples of 3?• 3, 6, 9, 12, 15, 18, 21, 24…
• The LCM of 4 and 3 is 12
LCM?
• So… if I were adding or subtracting two fractions, and their denominators were 4 and 3, I would have to get both of their denominators to be 12 (the LCM) before I continued!
Find the LCM Let’s do a few together!
• What is the LCM of 9 and 7?• 9, 18, 27, 36, 45, 54, 63…• 7, 14, 21,28, 35, 42, 49, 56, 63…• LCM of 9 and 7 is 63
• What is the LCM of 6 and 8?• 6,• 8,• LCM of 6 and 8 is
Let’s Go!
Adding and Subtracting Fractions
3 4
2 + 8
Step 1: Find the LCM of the denominators. The denominators are 4 and 8. 4, 8, 12, 16, 20, 24, 28…8, 16, 24, 32, 40, 48…The LCM is 8. You need to make 8 your new denominator.
Answer is
Adding and Subtracting Fractions
3 x 2 6 4 x 2 8
2 x 1 2+ 8 x 1 8
Step 2: Determine what times the old denominator gives you the new denominator. For example, What times 4 gives you 8? What times 8 gives you 8? Multiply the top and bottom by the same numbers.
Answer is
Adding and Subtracting Fractions
3 x 2 6 4 x 2 8
2 x 1 2+ 8 x1 8
8 8
Step 3: Add or subtract the new fractions with the same denominators. Remember – only add or subtract the numerators (top numbers)! We are adding how many eighths we have!6+2 = 8. We have eight eighths!
Step 4: Check to see if it needs to be simplified or reduced.
Answer is
ONLY COPY THE PROBLEM AND STEP 3
3 x 2 6 4 x 2 8
2 x 1 2+ 8 x1 8
8 8
Step 1: Find the LCM of the denominators.
Step 2: Multiply both the top and bottom by the same number so the denominator becomes the LCM.
Step 3: Add or subtract the new fractions with the same denominators. If there are whole numbers, add or subtract those next.
Step 4: Check to see if it needs to be simplified or reduced. 8/8 = 1!
Answer is
RememberRemember to check to see if your answer needs to be
simplified or reduced. For example, if your answer was 3 9Step 1: In order to simplify or reduce, find the GCF
(Greatest Common Factor) of 3 and 9. Factors of 3 are 1 and 3Factors of 9 are 1, 3, and 9 GCF =3Step 2: Divide the top and bottom by GCF 3 ÷ 3= 1 9 ÷3 = 3
Let’s Go!
Let’s Practice!2 1- + -7 2
Let’s Practice!2 1- + -7 2
What do we do first?Find the…
Let’s Practice!2 1- + -7 2
LCD of 7 and 2? 14!Let’s get both
denominators to be 14! How do we do that?
Let’s Practice!2 X 2 1 x
7--- + ---7 X 2 2 x 7
4 7--- + ---14 14
LCD of 7 and 2? 14!Let’s get both
denominators to be 14!
Now what do we add?
Let’s Practice!2 X 2 1 x
7--- + ---7 X 2 2 x 7
4 7--- + ---14 14
LCD of 7 and 2? 14!Let’s get both
denominators to be 14!
Now what do we add?
4+7=11
Answer= 11/14!
✔For Understanding • Go to your handout and
complete the adding and subtracting fractions 1-4. You will have 10 minutes.
Did you get the right answer? Don’t forget to simplify the fraction.
Quia
• You will have 15 minutes to show us what you know. Log onto Quia and take the quiz titled Fractions_March 4_2011.