Our objective today is to review Adding and

Subtracting Fractions.When I think of fractions, I always think of “Pizza.” Pizza will be our

theme today!

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Some Warm Ups

Write the following as fractions.

(1) 2 out of 5 slices have mushroom.

(2) Circles that are colored green.

(3) Circles that are not colored.

(4) There are 3 pies. 2 pies and three out of eight slices

of a third pie have anchovies.

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Estimating Sums and DifferencesA benchmark is a number used to replace

fractions that are less than 1.

We use a benchmark of 0, ½, and 1 when estimating sums and differences of fractions.

Description Examples Benchmark

Numerator is very small when compared to denominator

1/8, 3/16, 2/25, 9/100 0

Numerator is about one half of the denominator

3/8,9/16,11/25,52/100 1/2

Numerator and denominator are close to each other

7/8,14/16,23/25,95/100 1

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Let’s round the measurement inch by choosing a benchmark.

7 is half of 16

½ inch is the benchmark

Let’s round the measurement inch by choosing a benchmark.

1 inch is the benchmark

7 16

7 16

15 16

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Estimate 7 + 4 12 5

Replace each fraction with a benchmark 7 + 4 1 + 1 12 5 2 Add 1 ½

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Estimate

Estimate each sum or difference

(1) (2)

Replace each fraction with a benchmark 12 _ 2 1 - 0 13 25 Subtract 1

12 _ 2 13 25

11 _ 2 20 15

10 + 4 12 5

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Adding and Subtracting with Like denominatorsTo add or subtract fractions with like denominators, add (subtract) the numerators and keep the same

denominator.

Find

4 + 7 12 12

4 + 7 = 4 + 7 Add the numerators.

12 12 12 Denominators stay the same.

= 11 12

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(1) At a pizza place, 4/12 of a pepperoni pie and 7/12 of a vegetable pie were sold. How much more vegetable pies than vegetable pies were sold?

(2) Which solution to is correct? Explain your reasoning.

1 + 2 5 5

1 + 2 = 3 5 5 5

1 + 2 = 3 5 5 10

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Adding and Subtracting with Unlike denominators Write the fraction using a common denominator

Perform the operation in the numerator.

Denominators remain the same.

3 32 6 10 102 20 The LCD is 20. Write the fraction with the same denominator. + 1 15 + 5 4 45 20 11 Add the 20 numerators.

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Your Turn

1. The famous sauce recipe calls for ¼ cup of pepper and cups of oregano. How much more oregano than pepper is needed?

2. Find +

3. Find –

5 6

1 3

1 2

5 6

1 2

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Adding Mixed Numbers

You can find the sum of mixed numbers by adding the whole number and fractions parts separately. Then you combine the two parts to find the total.

Add 8½ + 6 ¼

8 8 LCD is 4. Write fractions with same denominator.

+ 6 + 6

______________

14 Add whole numbers, and then fractions.

1 2

2 4

1 4

1 4

3 4

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• Let’s take a break!

• How about a puzzle?

• Click here for puzzle!

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Your Turn

1. The depth of a pizza pan is 2 ½ cm deep. After baking the pizza rises 1 ¾ cm above the pan. How deep is the pizza? Remember to convert improper fractions to mixed number.

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Subtracting Mixed Numbers

• When you subtract mixed numbers, you need to write the fractions with a common denominator. Then you can subtract the whole numbers and the fractions separately.

1. Fresh vegetables are grown for toppings. Zesty tomatoes are taken from a plant that is 11 ¾ inches tall. A mushroom plant is 7 5/8 inches tall. What is the difference between the heights of the plants.

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Renaming a Whole Number

• Find 7 – 2

• How would you convert 7 to a mixed number? Remember to use 8 as the denominator in this case!

• 7 6 Rename 7 as 6 +1 = 6

- 2 - 2 Subtract the whole numbers. Then subtract the _____________ fractions.

4

5 8

8 8

5 8

5 8

3 8

8 8

8 8

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Your Turn 1. Giorgio made 10 pepperoni pies for lunch. He sold 7 ¼

pies. How many pies were left over from lunch?

2. Find 5 – 3

2 3

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Renaming a Mixed Number

Find 9 - 1

Here we face a problem. Using the LCD 8, the top numerator is smaller than the bottom numerator.

9 9 8 Rename 9 as 8 + 1 or 8

-1 -1 -1

_________________

7

1 8

3 4

1 8

1 8

3 4

6 8

9 8

6 8

1 8

8 8

9 8

3 8

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Your Turn

1. The vegetable man delivers 7 pounds of fresh, red, ripe tomatoes on Wednesday. 5 ¾ pounds of tomatoes were delivered on Tuesday. How much more tomatoes were delivered on Wednesday than Tuesday?

1 6

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Assessment

1. The benchmark for 4/5 is ______.

2. Using benchmarks 0, ½ and 1 estimate the sum of

3. Find each sum or difference

(a) (b)

4. Mario the delivery boy rode his bike miles to deliver his first order. His second order was miles. What was the total distance Mario rode his bike?

5.

8 + 3 9 7

7 - 3 8 8

3 + 9 20 20

2 3 1

5

3 – 3 4 8

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6. Out of 6 pizza pies, 2 did not have any toppings. How many pizza pies had toppings.

7. 25 - 8

2 5

1 3

5 9

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Don’t forget the dessert

8. Tony’s pizzeria is famous for its desserts. The following is the ingredients for its mouth watering recipe for its’ Chocolate Chip Cookie Pizza. This recipe serves 12.

(a) How much chocolate chips would be needed to serve 24 people?

(b) How much more chocolate chip dough is needed than caramel topping?

(c) What is the total amount of chocolate chip and pecan needed?

Ingredients:

2 2/3 cup refrigerated chocolate chip cookie dough1 1/7 cup chocolate chips1 1/2 cup pecans -- chopped1 ¾ cup caramel ice cream topping

This recipe for Chocolate Chip Cookie Pizza serves/makes 12

Congratulations, you really do understand all about

fractions!You did a wonderful job…Treat

yourself to some PIZZA!!