Transcript Adding and Subtracting fractions with LIKE denominators

Adding and Subtracting
fractions with LIKE
denominators
Grade 5
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1
How about some warm-ups?
Write each fraction in simplest form:
1. 10
40
2. 12
28
3. 8
24
4. 20
24
5. 7
12
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Let’s review some of the concepts of the last lesson!
Last time, we learned how to estimate the sums and differences of
fractions and mixed numbers.
We used benchmarks of 0, ½, and 1 to round fractions. Our
guidelines are as follows:



When numerator is much smaller than denominator round to  0
When numerator is almost half of denominator round to
½
When numerator is almost same as denominator round to  1
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Review

To estimate sums and differences of mixed numbers, round to the
nearest whole number.

If mixed number has a fraction of ½ or greater  round up to next
whole number.

If mixed number has a fraction less than ½  leave whole number
the same!
Very Well….Lets carry on to today’s lesson
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To add with like denominators, we can follow three
simple steps:
1.
2.
3.
Add the numerator.
Keep the denominator the same.
If we need to….Simplify!!
4 + 2 = 4+2 =6
7
7
7
7
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4
7
At a bake sale, 12 of a cherry pie and 12 of an apple pie are
sold. What is the total amount of pie sold?
4 + 7
12 12

In this problem we are asked to find the sum of

Our first step is to add the numerator.

Second step is to keep the denominator the same.
4 + 7 = 4 + 7 = 11
12
12
12 12

In this case the fraction is already simplified.
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Your Turn

Marie set out to bake a lemon meringue pie. The depth of a pie pan
that she used is 1 cm deep. After baking, the crust rises another 1
6
6
cm above the pan. How deep is Marie’s pie?
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Sometimes, the sum of fractions is greater than 1. In
this case we must rename the improper fraction, as a
mixed number.
7
5
 After the thanksgiving day dinner, 9 of a pecan pie and 9 of a
pumpkin pie were left. What fractions of the pies remain?
7 + 5 = 7+5
9
9
9
12
9

Combine numerators over
denominators.
 Add the numerators.
Denominators remain the same.
3
9

Write as a mixed number.
11
3

Simplify.
1
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You try this one!
3
7
 A mix fruit pie recipe calls for 8 cups of apples, and 8 cups of
cherries. What is the total amount of fruit that the recipe requires?
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Just like adding fractions with like denominators,
can also subtract with like denominators following
3 simple steps:
1.
2.
3.
we
Subtract the numerator.
Keep the denominator the same.
If we need to….Simplify!!
4 _ 2 = 4-2 = 2
7
7
7
7
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A pie is cut into eight equal pieces. Six slices are topped
with cherries. The two remaining pieces are topped with
walnuts. How much more of the pie is topped with cherries
than walnuts?

6
2
We are asked to find the difference between
8
8
6
2 = 6 - 2  Combine numerators
8
8
8
over denominators.
4  First subtract the numerators.
8
Denominators remain the same.
1

2
Write the fraction in simplest
form.
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You try this one!
A caterer orders 105 pies. The order includes 50 apple pies,
30 peach pies, and some cherry pies. What fraction of the
pies are cherry pies?
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Let’s take a break!
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Let’s try to do some unscrambling ….
Unscramble each of the clue words. Copy the letters in the numbered
cells to other cells with the same number.
Today’s lesson is
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Answers
1.
2.
3.
4.
5.
6.
NUMERATOR
DENOMINATOR
BENCHMARK
ESTIMATE
SUM
DIFFERENCE
Today’s lesson is A PIECE OF PIE.
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Assessment
1.
Greg, otherwise known as the “left-over-eater- upper,” is getting
ready to get his hands on the remains from the party. ¼ of the
apple pie and and ¼ of the cherry pie are left over. What are the
steps by which we can find the sum of the leftover pies that Greg
will eat?
2.
Add
2 + 4
9
9
3.
Add
3+ 3
4 4
4.
Subtract
7
8
1
8
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5.
8
Find 9 14 + 2 4
6.
Replace x to make the equation true.
14
7 _ x = 1
12 12 6
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7.
5
At Mario’s bakery, 20 of the customers purchased banana nut pie,
.3 of the customers purchased apricot pie, and 5 of the
20
20
customers purchased kiwi lime pie.
(a) What portion of the customers purchased either banana nut or
apricot pie?
(b) What is the difference in fractions between the customers who
purchased kiwi pie and apricot pie?
(b) What portion of the customers purchased another type of pie?
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Lets recap what we learned today!

Today we learned how to add and subtract fractions with like
denominators.

To add fractions with like denominators, we add the numerator,
and keep the denominator the same!

Sometimes, our sum is greater than 1. In this case, we
rename the improper fraction into a mixed number.
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
To subtract fractions with like denominators, we first subtract the
numerator, and leave the denominator the same.

Always remember to simplify, when needed!
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You did an excellent job today!
Remember to do the practice
sheets!!
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