## November: Addition and Subtraction of 2 and 3 digit Numbers

A. Students are learning to use different strategies to find basic facts.

They should know:

1. Doubles Facts (5+5, 8+8, etc..)

2. Sums of Ten (1+9 =10, 4+6=10, etc...)

3. Relate addition to subtraction like in Fact Families (6+7=13, 7+6=13, 13-7=6, 13-6=7 )

B. Students should be able to estimate addition and subtraction equations.

They have been shown 3 different ways to estimate.

67 + 32 = ?

Way # 1 Estimate by rounding each number to the nearest 10

67 rounds to 70 and 32 rounds to 30

70 + 30 = 100 The answer to 67 + 32 is about 100.

Way #2 Estimate by adding the numbers in the tens place.

67 has 6 tens

32 has 3 tens

6 tens + 3 tens = 9 tens or 90 The answer to 67 + 32 is about 90.

Way # 3 Estimate by rounding one of the numbers and then adding it to the other number.

67 rounds to 70

70 + 32 = 102 The answer to 67 + 32 is about 102.

***The students can use each of these estimating strategies to either add or subtract.

C. Students need to use personal strategies to add 2 and 3 digit numbers.

**Please note we are trying to stay away from using tradition algorythms (carrying and borrowing) to add and subtract because students usually do not understand what they are doing.

Strategy #1 Adding the place value

78 + 46 = ?

70 + 40 and 8 + 6 (Students add the tens together and then add the ones together.)

110 + 14

124

Strategy #2: Adding the place value in a stacking method

78

They should know:

1. Doubles Facts (5+5, 8+8, etc..)

2. Sums of Ten (1+9 =10, 4+6=10, etc...)

3. Relate addition to subtraction like in Fact Families (6+7=13, 7+6=13, 13-7=6, 13-6=7 )

B. Students should be able to estimate addition and subtraction equations.

They have been shown 3 different ways to estimate.

67 + 32 = ?

Way # 1 Estimate by rounding each number to the nearest 10

67 rounds to 70 and 32 rounds to 30

70 + 30 = 100 The answer to 67 + 32 is about 100.

Way #2 Estimate by adding the numbers in the tens place.

67 has 6 tens

32 has 3 tens

6 tens + 3 tens = 9 tens or 90 The answer to 67 + 32 is about 90.

Way # 3 Estimate by rounding one of the numbers and then adding it to the other number.

67 rounds to 70

70 + 32 = 102 The answer to 67 + 32 is about 102.

***The students can use each of these estimating strategies to either add or subtract.

C. Students need to use personal strategies to add 2 and 3 digit numbers.

**Please note we are trying to stay away from using tradition algorythms (carrying and borrowing) to add and subtract because students usually do not understand what they are doing.

Strategy #1 Adding the place value

78 + 46 = ?

70 + 40 and 8 + 6 (Students add the tens together and then add the ones together.)

110 + 14

124

Strategy #2: Adding the place value in a stacking method

78

__+46__

110 (70 +40)__14 (8 + 6)__

224