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Strategies for Operations
 

Add-Subt Strategies

 Mult-Strategies

 Div-Strategies

Posters for Addition and

  Subtraction Strategies

                        Posters for 

             Multiplication Strategies

                    Posters for 

              Division Strategies

 
       Addition        Subtraction        
 

Counting On
Counting on is used when adding 1, 2, or 3. Students say or think the larger number and count on 1, 2, or 3. It is inefficient to use counting on with numbers greater than 3 because it is difficult to keep more than 3 numbers in the head.

Add-CountOn

Doubles
Doubles are the addition facts where a number is added to itself. These need to be memorized through double 10.

Add-Doubles

Doubles Plus One
Students use their knowledge of doubles to figure out harder problems. If you know that 7 + 7 = 14, then 7 + 8 would be one more, 15. Students need to know their doubles facts to be able to do this, and they need to be able to identify when they can use doubles plus one. We talk about numbers that are next to each other on the number line – next door neighbors. If the numbers are next to each other, you can use the doubles plus one strategy to solve.

Add-DoublesPlusOne 

Doubles Plus Two
If you know that 7 + 7 = 14, then 7 + 9 = 16

Add-DoublesPlusTwo 

Or students may use the strategy …

Double the Skipped Number
Students recognize these facts because the numbers are two apart, or a number is skipped if counted in sequence. Examples are 6 + 8 and 7 + 9. To solve these problems, students double the number that is skipped.

Add-DoubleSkippedNumber    

Adding to Make Ten
Students need to be familiar with the combinations that make ten. Look at the pattern of these combinations, as well as using a ten frame to see the combinations.

 

Add-ToMake10 

Adding with Tens
Students should be able to add 10 to any number. This skill helps to facilitate the next strategy (adding 8 and 9). It also aids basic place value understanding.

 

Add-WithTens 

Adding 8 and 9
This is a strategy that builds on the “adding to make ten” skill. Students use a ten frame (or visualize the ten frame) and mentally make the 9 into a 10, so that they can think “10 + ___.”

 

Add-9 

 

The same strategy is used with visualizing 8 in the ten frame. Students mentally move two into the ten frame to make ten and then are able to add “10 + ___.” Adding 8 is more difficult, and second graders may not grasp it right away.

 

Add-8

 

 

          

Zeros

This is the understanding that any number minus itself is zero and any number minus zero is itself.

Zero

Counting Up

Counting up is used when the numbers are close to each other on the number line; in other words, when the difference between two numbers is three or less. Students determine the difference by counting up from the smaller number to the larger number. The answer is how many times you counted up.

CountingUP

Counting Back
Counting back is used when subtracting 1, 2, or 3. Students whisper or think the larger number and count back 1, 2, or 3. It is inefficient to use counting back with numbers greater than 3 because it is difficult to keep more than 3 numbers in your head.

 

CountingBack

 

Doubles
Doubles are subtraction facts in which the larger number is double the number being subtracted. These need to be memorized through 20.

 

Doubles

 

Using Doubles to Subtract
This strategy is used when the part being subtracted is close to half of the number from which you are subtracting. Students think of the addition double and then count up to get to the larger number.

 

DoublesToSubtract

 

 

Think Addition
If students know their addition facts, they can use that knowledge to solve subtraction facts. This concept can be introduced in several ways:

 

UseAdditonFacts

 

 

Subtracting from 10
Students use a ten frame (or visualize the ten frame) and use their knowledge of "sums to ten" to subtract.

Subtacting10

Sutracting from 9
If students know their sums of ten, they can use the same knowledge to subtract from 9.

SubtractingFrom9

Make Ten and Then Some
This strategy builds onthe adding to make ten strategy. Students use a ten frame (or visualize the ten frame) and mentally add to make ten, then add onto get the total (minuend).

Make10ThenSome 

 

 

 

 

 

 

 
 

Summarization of Some Addition Strategies

 

Addition Strategies

 

 More Subtraction Strategies 

 Click on image to download PPT

  Subtraction-More

     

Activities and teaching suggestions are provided in the Addition and Subtraction Fact Strategies booklet from the Wichita Public Schools.

 

Children should have multiple experiences with all the common addition and subtraction situations

 
 

 

 

 

 
 

Multiplication

 

Division

 
 

 

Basic Facts

 

Please note that this list of strategies is not comprehensive.  The examples of basic fact strategies are given as an instructional sequence that focuses on connecting multiplication to known addition facts.  The list begins with the easiest multiplication fact strategies and moves towards the more difficult.  

 

Students need to fully understand the commutative property, and "turnaround" facts should be presented together. Arrays are important tools to use as students are building a conceptual understanding of multiplication.

 

Doubles (x2)  

Doubles in multiplication connects to doubles in addition. These facts are relatively easy to learn, especially if students already mastered the doubles for addition. 

Mult x2

 

Fives (x5)

These multiplication facts are usually easy for students to master because of their experience skip counting by 5s.

Mult x5

 

Zeros and Ones (x0 or x1)

Make sure to differentiate addition concepts from multiplication concepts for these facts.  They are often confused.  For example 6 x 0 is confused as 6 + 0.

 

Students can reason for these facts.  

  • For the zeros facts, any number multiplied by 0 is 0 because there would be no sets/groups, or there would be a certain number of sets/groups each with 0 objects.  
  • For the ones facts, any number multiplied by 1 equals that number because there is just one group/set of that number.

   

These facts are best developed using story problems to convey meaning rather than isolated rules such as "any number times 0 equals 0" or "any number times 1 equals that number."

 

Mult x0 or x1

Tens (x10)

These multiplication facts are usually easy for students to master because of their experience with standard 1.NBT.2c (The numbers 10, 20, 30, 40, 50, 60, 70, 80, 90 refer to one, two, three, four, five, six, seven, eight, or nine tens (and 0 ones) and standard 2.NBT.2 (Count within 1000; skip-count by 5s, 10s, and 100s).

Mult x10

 

Nines (x9)

Multiplying by 9 is like multiplying by 10 then taking one set away.

Mult x9

 

Focus on the patterns in these facts.  One pattern is the sum of the digits in the product is always equal to 9. The other pattern is the ten’s digit is always one less than the factor multiplied by 9.

 

 

For example, 9 × 6 = 54.

 

 

Notice 5 + 4 = 9 and the 5 in the product is one less 6, the number being multiplied by 9.

 

Another example, 8 x 9 = 72.

 

Again, the sum of the digits 7 and 2 is 9 and the tens digit is one less than the tens digit.

 

Double, Double (x4)

Because 4 is 2 doubled, multiplying by 4 is doubling doubles.

Mult x4

 

Square Numbers 
 

When making arrays, encourage students to make squares.  Have them recall that a square has the same number of units on each side.  This activity will help them visualize the products of 3 x 3, 4 x 4, 5 x 5, etc.

Mult SqNo

 

Remaining Facts

Use decomposition strategies, known facts, and the distributive property to solve.  For instance, 7 × 6 might be rewritten as 7 x (5 + 1). This would allow a student to use the 7 × 5 fact that he knows and add that to the 7 × 1 fact to get 42.

 

Activities and teaching suggestions are provided in the Multiplication Fact Strategies booklet from Wichita Public Schools.

 

Beyond the Basic Facts

 

Students need to demonstrate fluency of the basic multiplication (and addition!) facts before moving into multiplication of larger numbers.  And they need to develop conceptual understanding of multiplication of larger numbers before being introduced to the traditional multiplication algorithm.  There are several models and strategies that help them develop conceptual understanding.

 

Base-ten Model

The base-model for multiplication is an extension of the base-ten models children used to build and represent numbers. Using base-ten blocks, students can model the multiplication of a one-digit by a two-digit number. The model reinforces finding the area of rectangles.

 

Mult-Base10

 

Area Model

After having had experiences building base-ten models for multiplication, students can move to area models without the manipulatives.  The area models are representations which simplify by drawing rectangles rather than seeing all of the units as with the base-ten model.  Areas of component rectangles are found and then summed to find the product.

 

Mult-Area

The area model connects to algebra and the multiplication students with perform with binomials in later grades.

 

Mult-Alg

 

 

Intersection Model

The intersecton model of multiplication has its foundation in the array model.  The example below shows a basic fact, but the model can be extended for multiplying larger numbers.

 

Mult-IM1

 

In multiplying larger numbers using the intersection model, students must expand the factors using place value and use the distributive property to multiply all components.  Finding the product of 47 and 53 is found using the intersection model in two ways in the examples shown below.  

 

Mult-IM2

 

Mult-IM3

 

 

Partitioning Strategies 

Students can multiply two factors by using the distributive property and expanding a factor using place value.

 

Mult-PV1

 

 

Mult-PV2

 

 

Partial Products 

The use of the partial products strategy provides the foundation for the traditional algorithm.  Parial products requires students to use the distributive property and place value as they did with partitioning strategies, and it begins to put the work in place as students will do with the traditional algorithm.

 

Mult-PP1

 

Mult-PP2

 

Lattice Method

The lattice method is also connected to the distributive property and place value, but its connection is less obvious. When students draw the "lattice" it seems a bit similar to the area model, but it differs in that it does not require students to find the areas of rectangles.  Instead, students are multiplying the digits and using the lattice to keep the digits with the same place value aligned.

 

Mult-LM1

 

Mult-LM2

 

 

 

 

Basic Facts

  

Mastery of multiplication facts and connections between multiplication and division are the key elements of division fact mastery.  

 

Div BasicFacts

 

If students have trouble with this strategy, it is best to work on the related multiplication facts and developing efficient multiplication strategies.  Drill and practice of division facts without efficient strategies for related multiplication facts is ineffective.

 

Do not introduce premature drill and practice of division facts until students have mastered and own efficient strategies for related multiplication facts.  Counting on fingers or making marks on paper can never result in quick fact recall regardless of the amount of drill.  Drill without an efficient strategy present offers no benefit to students and merely reinforces inefficient practices.

 

Beyond the Basic Facts

 

Students must continually be challenged to consider the magnitude of numbers and whether or not the results they obtain are reasonable.  Estimation is a skill that is useful for all computations, but it is especially useful with division.  Having students predict the size of the quotient before carrying out any computations and then defend why they believe their prediction is reasonable is a good exercise in making sense of the work and in recognizing when results are out of bounds.  

 

As we begin a discussion of division beyond the basic facts, it is also important to recognize the two types of division:

  • Partitive division where the group size is unknown.  For example, "Twelve oranges are to be sorted equally into three bags. How many oranges will there be in each bag?"
  • Quotative division where the number of groups is unknown. For example, "Twelve apples have been placed into bags.  There are three apples in each bag.  How many bags are there?"  

 

The partitive type of division allows children to share the amount into groups equally until all the amount (or as close to it as possible) is gone.  An example of partitive division is illustrated below.

 

Mult-Partitive

 

Partitive division can be done for smaller numbers, but when the divisor (the number of groups) or the dividend (the amount being shared equally) get very large, it becomes less efficient and more tedious.  Other methods and strategies can be employed instead.  

 

The methods and strategies discussed below should be used to develop children's conceptual understanding of division of larger numbers before introducing them to the long division algorithm.

 

Area Model 

The area model for division is closely related to the area model for multiplication.  With multiplication, the product is the area of the large rectangle formed with consecutive sides the length of the factors.  The factors are known and the area (product) is found.  With division, the area of the rectangle (the dividend) and one of the sides (the divisor) are known, and the goal is to find teh length of the other side of the rectangle (the quotient).

 

Students begin by building the rectangle represented by the dividend using base-ten blocks, as in the example below.  

 

Div-AM1

 

 

 

Because 12 is the divisor, the rectangle has to have 12 as the length of one side. 

 

 

Div-AM2

 

 

The length of the other side of the rectangle is the quotient.

 

 

Div-AM3

 

 

In this case, the length of the edge consecutive to the edge of length 12 is 23.  Therefore, the quotient of 276 divided by 12 is 23.

 

The area model can also be used when there is a remainder.  It will become obvious that there is a remainder when it is impossible to build a rectangle of the dividend having the divisor as the length of an edge. Students will have to make sense of what to do with the remainder based on the context of the problem.

 

Decomposing the Dividend

A strategy for developing conceptual understanding of division is decomposing the dividend.  In this strategy, the student will rewrite the dividend as the sum of "friendly" numbers in relationship to the divisor.  Then the division is accomplished by dividing each part.  An example is shown below.

 

Div-DD

 

 

Partial Quotients

Partial quotients is a similar strategy to decomposing the dividend, and it provides the foundation for understanding the long division algorithm.  As students become more and more efficient with partial quotients, they are actually performing long division by the algorithm.

 

Partial quotients is based on the idea of division as repeated subtraction, using powers of ten to speed up the process.  An example of dividing using partial quotients is shown below.

 

Div-PQ

 

Here, the student is not yet efficient in finding the greatest number of times 84,000 can be divided by 27 and resorts to subtracting out several multiples of 1000 instead. 

 

When the difference gets to 3,926, the student uses a multiple of 100 to further reduce the amount.  

 

At a difference of 1,226, the student uses a multiples of 20 to reduce further.  Finally, the student uses a multiple of 5 to get a difference of 11, which is smaller than the divisor and is the remainder.  The quotient is the sum of all the multiples. In this case, 84,926 divided by 27 is 3,145 with a remainder of 11.

 

As illustrated in this example, multiples of 10, 100, and 1000 are the easiest ones for students to use as they divide using the partial quotients strategy.  Because multiplying by 2 and by 5 are relatively easy for students, they will often use multiples of 20, 200, and 2000 or 50, 500, and 5000 as well.

 

 

Children should have multiple experiences with all the common multiplication and division situations.