K-3 Flexible StrategiesLet the Adventure Begin!

Flexible StrategiesThe goal when using these strategies is to

eventually be able to add and subtract mentally. With mental math you can manipulate or change

a number to make an easier equation.This will take practice, confidence, and fluency

with facts. We will be looking at strategies that encompass

K-3rd Grade. It is important that you are aware of all strategies, because either your students will be coming in with these strategies or they will need to know them in the grades above you.

Addition/Subtraction Flexible Strategies

Task: Using one of these Addition or Subtraction Strategies, at your table create a poster for the strategy.

Post on the wallTake your passport

with you on your gallery walk.Fill in pg. 2-10 in your

passports

Addition and Subtraction Strategies

Composing NumbersDecomposing

NumbersCount OnCount BackMake a TenDoubles10 PlusBridge a 10Manipulatives/Base 10

Flexible Strategies for 2 or more Digits: Using Manipulatives

56 + 17= ?

https://learnzillion.com/student/lessons/2528-add-within-100-using-base-ten-blocks

Addition and Subtraction Flexible Strategies

Friendly Number Strategy

Friendly numbers are numbers that are easy to use in mental math.

To make a friendly number you can change one addend by adding to get that number to a five, multiples of 10,or monetary amounts such as 25 or 50.

**Remember to take away that same number at the end.

https://learnzillion.com/lessons/2798-add-up-to-four-2digit-numbers-by-using-addition-facts-and-friendly-numbers

11

Friendly Number Strategy

52+29=?

+30=82

29 is just one away from 30. Add 1 to make it easier to add by tens.

Take away one at the end to get back to the original problem.

This number stays the

same.

52+1

-181

Friendly Number Practice

35+78=? +2

35+80=115 -2 113

63+8=? +2

63+10=73 -2

71

Friendly Number with Larger Numbers

299 + 548= +1300 + 548= 848 -1 847

345+238= +5 +2350+240=590 -7 583

Addition and Subtraction Flexible Strategies

Expanded FormEach addend is broken into expanded form

and like place value amounts are added or subtracted.

This strategy allows the student to decompose numbers and become more proficient with place value while adding.

12-13

Expanded Form- Addition 36 + 57= 30 + 50= 80

6 + 7= 13 (10+3) 93

First decompose the numbers into

just the tens. Then add them together

Then add the ones together

The 13 can be broken

down too if it helps the student.

The sum is found by adding

the tens and ones together.

Expanded Form- Subtraction

52 - 28=? 50 – 20= 30

2 – 8=

20 + 4= 24

The numbers are broken into decades (tens) and ones.

The tens are subtracted first. Then you subtract the ones.

If you can’t do so, you need to ungroup one of the tens and add this to the ones.

Subtract the ones and then add the tens remainder and the ones remainder together.

First decompose the numbers into just the

tens. Subtract one ten from the

other.

When you “ungroup” the tens to add to the ones, you

rewrite the tens.

Add the tens and ones

back together to

get your answer.

Once you realize you don’t have

enough ones, you need to “ungroup” a

ten.

1 420

Expanded Form Practice64 + 39= ?60 + 30= 904 + 9= 13 (10+3) 90 + 13=103 or… 90+10=100 100+3=103

81 - 39=?80 - 30= 50 40 11 - 9= 2

40 + 2= 42

Addition and Subtraction Flexible Strategies

Estimation with Compatible Numbers

Estimate- a number close to an exact solution. Tells about how much or about how many.

Compatible Numbers- Numbers that are easy to work mentally.

Resource: star.spsk12.net/math/4/compatiblenumbers.ppt

14

Estimation with Compatible Numbers

Step 1: Round both numbers to a compatible number that is easy to work with in your head.

Step 2: Add or subtract the rounded numbers

83+19=

80+20=100

162 + 15 + 90=

200 + 20 + 90= 310

Estimation with Compatible Numbers Practice

Using your practice sheet, Power Teach these problems to a

partner at your table.

88 + 68 =

58 – 39 =

152 + 26 + 7 =

368 – 227 =

Addition and Subtraction Flexible Strategies

Open Number Line or Jump Strategy

The jump strategy makes “jumps” on an empty number line.

One number remains whole and the other number is broken into amounts that make it easier to add or subtract.

https://learnzillion.com/student/lessons/1583-solve-subtraction-problems-using-a-number-line 15-

16

Open Number Line

Problems can be solved in many different ways!

https://learnzillion.com/student/lessons/2540-subtract-numbers-within-100-using-an-open-number-line

Open Number Line7+5=

7

10

8

7

9 10 11

12

12

+2+35

+1 +1 +1 +1 +1 5

Open Number Line-Addition

54+38=?

54+38=?

54 64 74 84 90 92

+10

+10

+10

+6 +2

54 84 90 92

+30

+6 +2

Open Number Line- Subtraction

84-38=?

84-38=?

38 48 58 68 78 84

+10

+10

+10

+10

+6 46

84807060504038

-10-10-10-10-2 -446

Open Number Line Practice45+28=

45 55 65 70 73

+10

+10

+5 +3

82-47=

47 57 67 77 80 82

+10

+10

+10

+3 +2 35

Open Number Line with Larger Numbers

http://learnzillion.com/student/lessons/3057-add-using-an-open-number-line

http://learnzillion.com/student/lessons/3123-subtract-using-an-open-number-line

361 461 561 571 581 591 601 604

+3

+100 +10

+10 +10

+10+100

361+243=

Videos:

Addition and Subtraction Flexible Strategies

Compensation

You take away from one addend and add it to the other addend.

This changes one to the next decade number and you add the remaining to that decade number.

This strategy works best when you only have to compensate by one or two numbers. 17-18

Compensation- Addition

38 + 54= ? +2 -2 40 + 52= 92

Add 2 to get to the next

decade number. This will make it

easier to add.

Take 2 from this number to add it to the other

number. This keeps the value the

same.

Compensation- Subtraction

In subtracting it is

called a give/give or take/take

If you give to one digit, you must give to the other.

If you take from one digit, you must take from the other

Give/Give: 9 - 4=(give)+1 +1 (give)

10 - 5=5Take/Take: 11 - 4= (take) -1 -1 (take)

10 - 3=7

Compensation- Subtraction

Review: When you: give/take give/give take/take

46 - 29= +1 +1 (give/give)

47 - 30= 17

addingsubtractingsubtracting

Compensation Practice with Larger Numbers

452-197= +3 +3 (give/give)

455-200=255

299+548= +1 -1 (give/take)

300+547=847

Compensation Practice59 + 24 =

88 - 37 =

299 + 548 =

452 – 197 =

Using your practice worksheet, Power Teach these problems to a partner at your table.

Word ProblemJack has 42 cents in his bank. His mom gives him 28 more cents. How much

does Jack have now?

Solve on your practice sheet using the strategy of your choice.

Take 3 giant steps, to find a person NOT at your table. Stand back to back.

Now, turn around and share how you each solved the problem.