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Flexible Strategies The 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-3 rd 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 wall Take your passport with you on your gallery walk. Fill in pg in your passports Addition and Subtraction Strategies Composing Numbers Decomposing Numbers Count On Count Back Make a Ten Doubles 10 Plus Bridge a 10 Manipulatives/Base 10

Flexible Strategies for 2 or more Digits: Using Manipulatives = ? using-base-ten-blocks 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. four-2digit-numbers-by-using-addition-facts-and- friendly-numbers 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

Friendly Number Practice 35+78=? = =? =

Friendly Number with Larger Numbers = = = =

Addition and Subtraction Flexible Strategies Expanded Form Each 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

Expanded Form- Addition = = = 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 =? 50 – 20= 30 2 – 8= = 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

Expanded Form Practice = ? = = 13 (10+3) =103 or… 90+10= = =? = = = 42

Expanded Form with Larger Numbers Addition : = = = = = =847 add-threedigit-numbers-using-expanded-form Subtraction: = subtract-threedigit-numbers-using-expanded-form =282

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= = = 310

Estimation with Compatible Numbers Practice Using your practice sheet, Power Teach these problems to a partner at your table = 58 – 39 = = 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. subtraction-problems-using-a-number-line subtraction-problems-using-a-number-line 15-16

Open Number Line Problems can be solved in many different ways! ssons/2540-subtract-numbers- within-100-using-an-open-number- line

Open Number Line 7+5=

Open Number Line-Addition 54+38=?

Open Number Line- Subtraction 84-38=?

Open Number Line Practice 45+28= =

Open Number Line with Larger Numbers ons/3057-add-using-an-open- number-line ons/3123-subtract-using-an-open- number-line = 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

Compensation- Addition = ? = 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) (give) =5 Take/Take: = (take) (take) =7

Compensation- Subtraction Review: When you: give/take give/give take/take = (give/give) = 17 adding subtracting

Compensation Practice with Larger Numbers = (give/give) = = (give/take) =847

Compensation Practice = = = 452 – 197 = Using your practice worksheet, Power Teach these problems to a partner at your table.

Word Problem Jack 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.