Adding and Subtracting Whole Numbers This is a powerpoint presentation about how to add and subtract positive whole numbers without the use of a calculator.

Benchmark MA.2.A.2.1: Recall basic addition and related subtraction facts. MA.2.A.2.2: Add and subtract multi-digit whole numbers through three digits with fluency by using a variety of strategies, including invented and standard algorithms and explanations of those procedures.

Objectives Review of basic subtraction facts. Develop fluency with multi-digit addition and subtraction.

Subtraction

Subtraction Facts Subtraction is removing some objects from a group. The meaning of 5 – 3 = 2 is "Three objects are taken away from a group of five objects and two objects remain". Examples: 6 - 2 = 4 9 - 3 = 6

Subtraction Example Example: 8 - 3 This is the subtraction of 3 from 8 or 8 minus 3 Subtraction is represented as shown: 8 - 3 We can count down to get the difference 8  7, 6, 5 so the difference is 5 3

What is Subtraction? Subtracting whole numbers is the inverse operation of adding whole numbers.

Relationship between Addition and Subtraction There is an inverse relationship between addition and subtraction. If a math fact is considered, for example 3 + 7 = 10. Then the following are also true: 10 - 3 = 7 10 - 7 = 3 Similar relationships exist for subtraction, for example 10 - 3 = 7. Then the following are also true: 3 + 7 = 10 7 + 3 = 10

Subtraction word problem Mika is 6 years younger than her cousin Ben. Ben is 11 years old, how old is Mika? Mika is 5 years old Mika is 6 years old Mika is 4 years old Mika is 7 years old

Subtraction facts Subtractions with one digit are usually fairly easy. Things start getting complicated when you have more than one digit and you cannot remove the number at the bottom from the number on top such as when doing 85 − 8

Two-Digit Subtraction What is 76 – 23? Let’s use the 100 Chart

Two-Digit Subtraction (cont.) What is 76 – 23? Start at 67. 23 is 2 tens 3 ones Let’s count back in the 100 chart 2 tens and then 3 ones

Two-Digit Subtraction (cont.)

Examples 83 – 50 = ____ 22 – 14 = ____ 46 – 15 = ____ 31 – 15 = ____ 73 – 26 = ____

Word Problem There were 32 birds in the trees. Then 15 birds flew away. How many birds are in the trees now?

Break Apart Approach Breaking Apart makes subtraction easier. Example: 63 – 7 = ___ 7 Subtract 3 to get 60. Then subtract 4 more. 63 – 7 = 63 – 3 – 4 = 60 – 4 = 56 3 4

Examples Use the Break Apart strategy to find the difference: 75 – 7 = _____ 82 – 5 = _____ 76 – 9 = _____ 85 – 8 = _____

Subtraction by Regrouping What is 42 – 15? Step1: Are they enough ones to subtract 5? No. Step 2: Regroup 1 ten as 10 ones.

Subtraction by Regrouping (cont.) Step3: Subtract the ones. 12 – 5 = 7 Step 4: Subtract the tens. 3 – 1 = 2

Subtraction by Regrouping (cont.) The difference is then: 27

Example Since you could not remove 8 from 5, you borrowed a ten from 8 tens and add that to 5 to make it 15

Word Problem Jane and her mom made 33 puppets for the craft fair. By noon, they had sold 14 of the puppets. How many puppets did they have left to sell?

Solve the Following Problems 89 - 25 50 - 9 99 - 12 69 - 35