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
+46
110 (70 +40)
14 (8 + 6)
224
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