Addition and Subtraction
Mar 29, 2015
Addition and Subtraction
Do not train children to learning by force and harshness, but direct them to it by what amuses their minds, so that you may be better able to discover with accuracy the peculiar bent of the genius of each.
Plato
Arithmetic Today Arithmetic has generally been learned
through basic algorithms, but it has great potential through problem solving techniques.
Current Traditional Algorithm
Addition1
47+28 75
“7 + 8 = 15. Put down the 5 and carry the 1. 4 + 2 + 1 = 7”
Subtraction 7 13
83- 37 46
“I can’t do 3 – 7. So I borrow from the 8 and make it a 7. The 3 becomes 13. 13 – 7 = 6. 7 – 3 = 4.”
Expanded Column Method
Number Line Method
Add on Tens, Then Add Ones
46 + 38
46 + 30 = 76 76 + 8 = 76 + 4 + 4
76 + 4 = 8080 + 4 = 84
Partitioning Using Tens Method
Nice Numbers Method
Lattice Method
First arrange the numbers in a column-like fashion.
Next, create squares directly under each column of numbers.
Then split each box diagonally from the bottom-left corner to the top-right corner. This is called the lattice.
Now add down the columns and place the sum in the respective box, making the tens place in the upper box and the ones place in the lower box.
Lastly, add the diagonals, carrying when necessary.
Counting Down Using Tens Method
Partitioning Using Tens Method
Nice Numbers Method
The Counting-Up Method
The Counting-Up Method
Nines Complement
827 → 827
- 259 → 740 (nines complement)
+ 1 (to get the ten's complement)
1568
568 (Drop the leading digit)
Benefits of Alternative Algorithms
Place value concepts are enhanced They are built on student understanding Students make fewer errors
Suggestions for Using/Teaching
Traditional Algorithms We are not saying that the traditional algorithms
are bad. The problems occur when they are introduced
too early, before students have developed adequate number concepts and place value concepts to fully understand the algorithm.
Then they become isolated processes that stop students from thinking.
Integers
Integers can be easily approached by thinking in regards of basic addition/subtraction and determining its position on the number lineIs the final result positive or negative?
Integer Addition Rules
Rule #1 – If the signs are the same, pretend the signs aren’t there. Add the numbers and then put the sign of the addends in front of your answer.
9 + 5 = 14-9 + -5 = -14
Integer Addition Rules
Rule #2 – If the signs are different pretend the signs aren’t there. Subtract the smaller from the larger one and put the sign of the one with the larger absolute value in front of your answer.
-9 + 5 =
9 - 5 = 4
Larger abs. value
Answer = - 4
One Way to Add Integers Is With a Number Line
0 1 2 3 4 5 6-1-2-3-4-5-6
When the number is positive, count to the right.
When the number is negative, count to the left.
+-
One Way to Add Integers Is With a Number Line
0 1 2 3 4 5 6-1-2-3-4-5-6+
-
+3 + -5 = -2
One Way to Add Integers Is With a Number Line
0 1 2 3 4 5 6-1-2-3-4-5-6
-
+
-3 + +7 = +4
Adding Integers with Tiles
We can model integer addition with tiles. Represent -2 with the fewest number of
tiles
Represent +5 with the fewest number of tiles.
ADDING INTEGERS What number is represented by combining
the 2 groups of tiles?
Write the number sentence that is illustrated.
-2 + +5 = +3
+3
ADDING INTEGERS
Use your red and yellow tiles to find each sum.
-2 + -3 = ?
+ = -5
ADDING INTEGERS -6 + +2 = ?
+ = - 4
+ = +1
-3 + +4 = ?
SUBTRACTING INTEGERS
We often think of subtraction as a “take away” operation.
Which diagram could be used to compute
+3 - +5 = ?
+3 +3
SUBTRACTING INTEGERS
We can’t take away 5
yellow tiles from this
diagram. There is not
enough tiles to take
away!!
This diagram also represents
+3, and we can take away +5.
• When we take 5 yellow tiles
away, we have 2 red tiles left.
SUBTRACTING INTEGERS
Use your red and yellow tiles to model each subtraction problem.
--2 - 2 - --4 = ?4 = ?
SUBTRACTING INTEGERS
This representation
of -2 doesn’t have
enough tiles to
take away -4.
Now if you add 2 more reds
tiles and 2 more yellow tiles
(adding zero) you would
have a total of 4 red tiles and
the tiles still represent -2.
Now you can take away 4 red tiles.
-2 - -4 = +2
2 yellow tiles are left, so the answer is…
SUBTRACTING INTEGERS
Work this problem.
+3 - -5 = ?
SUBTRACTING INTEGERS
• Add enough red and yellow pairs so you can take away 5 red tiles.
• Take away 5 red tiles, you have 8 yellow tiles left.
+3 - -5 = +8
Although children learn addition of whole numbers with ease, addition of fractions — though conceptually the same as addition of whole numbers — is much harder.
It requires knowledge of fraction equivalencies.
To add two fractions, you have to know that they must be thought of in terms of like units.
We take this for granted when we add whole numbers: 3 + 5 is really 3 ones + 5 ones
— but not when we add fractions: 3 halves + 5 fourths is, for purposes of addition, 6 fourths + 5 fourths.
Why is adding fractions a difficult concept for students to grasp?
Let’s Eat Pizza
The pizza is currently 8 pieces
What if I wanted to eat one eighth of the pizza?
One fourth of the pizza?
One sixteenth of the pizza?
One twelfth of the pizza?
Addition of Fractions
The objects must be of the same type We combine bundles with bundles and sticks
with sticks.
Addition means combining objects in two or more sets
In fractions, we can only combine pieces of the same size
In other words, the denominators must be the same
Click to see animation
+ = ?
Example:
Addition of Fractions
8
3
8
1
Example:
Addition of Fractions
+ =
8
3
8
1
+ =
Example:
The answer is which can be simplified to
Addition of Fractions
8
3
8
1
8
4
8
)31(
2
1
Addition of Fractions with equal denominators
More examples
5
1
5
2
5
3
10
7
10
6
10
13
15
8
15
6
15
14
10
31
With different denominators
In this case, we need to first convert them into equivalent fraction with the same denominator.
Example:
15
5
53
51
3
1 15
6
35
32
5
2
5
2
3
1
An easy choice for a common denominator is 3×5 = 15
Therefore,
15
11
15
6
15
5
5
2
3
1
Addition of Fractions
• When the denominators are bigger, we need to find the least common denominator by factoring.
• If you do not know prime factorization yet, you have to multiply the two denominators together.
With different denominators
Addition of Fractions
More Exercises:
8
1
24
23
8
1
4
3
7
2
5
3
9
4
6
5
=
=
=
57
52
75
73
69
64
96
95
=
=
=
8
1
8
6=
8
7
8
16
35
10
35
21
35
31
35
1021
=
54
24
54
45
54
151
54
69
54
2445
=
Subtraction of Fractions Subtraction means taking objects away
Objects must be of the same type we can only take away apples from a
group of apples
In fractions, we can only take away pieces of the same size. In other words, the denominators must be the same.
Subtraction of Fractions
Example:
12
3
12
11
This means to take away
12
11
take away
equal denominators
12
3
12
311
12
3
12
11
3
2
12
8
More examples:
16
7
16
15
16
715
2
1
16
8
9
4
7
6
79
74
97
96
63
28
63
54
63
2854 26
63
23
11
10
7
1023
1011
2310
237
2310
1011237
230
110161
230
51
Did you get all the answers right?
Subtraction of Fractions
Adding/Subtracting
38 8
138 4
1= =-- 18
882=
c
ba
c
b
c
a Fraction Addition/Subtraction
Fraction Simplification
2811 2
7+ ++
=
==
Common Denominator = ??????
28
2811
7
244
2811
288
28+11 8 =
2819
c
ba
c
b
c
a Fraction Addition/Subtraction
???728
211
Adding/Subtracting
Fractions: Steps for Success
1. Know the fraction rules and how to apply them
2. Show your work and write out each step3. Check your work for errors or careless
mistakes