2-Digit addition and subtraction
Addition:
Children use several processes in the beginning stages of building understanding of addition.
* Understanding and mastering the basic facts support children's success with 2-digit addition.
* For sums less than 10, children may apply counting processes.
* For sums greater than 10, children may use strategies such as make a ten.
* Realizing that strategies used for 1-digit addition are not efficient for 2-digit addition, children may invent their own strategies.
Ten (10) is important as a benchmark number in mathematics, not only for counting but also for addition. Children's early development of learning to count by 10 brings rewards in two-digit addition.
* A compensation strategy cab be used to add 2-digit numbers when one addend is near the next ten. For example, 48 + 17 can be added by adding 2 to the 48 and subtraction 2 from 17, resulting in 50 + 15.
* Such strategies are grounded in children's ability to make use of prior knowledge of counting by tens and recognizing two-digit numbers with zero in the ones place are east to add.
Subtraction:
The standard algorithm for subtracting numbers that require regrouping can be difficult for children to master.
* Modeling the algorithmic process with manipulative such as base-ten blocks helps children to understand the regrouping process.
* If children are familiar with the term "borrowing" to describe the regrouping that takes place, modeling will help them see that regrouping, or trading, better describes the process.
* Explaining modes and recording what they show will strengthen children's conceptual and procedural understanding of 2-digit subtraction.
Children use several processes in the beginning stages of building understanding of addition.
* Understanding and mastering the basic facts support children's success with 2-digit addition.
* For sums less than 10, children may apply counting processes.
* For sums greater than 10, children may use strategies such as make a ten.
* Realizing that strategies used for 1-digit addition are not efficient for 2-digit addition, children may invent their own strategies.
Ten (10) is important as a benchmark number in mathematics, not only for counting but also for addition. Children's early development of learning to count by 10 brings rewards in two-digit addition.
* A compensation strategy cab be used to add 2-digit numbers when one addend is near the next ten. For example, 48 + 17 can be added by adding 2 to the 48 and subtraction 2 from 17, resulting in 50 + 15.
* Such strategies are grounded in children's ability to make use of prior knowledge of counting by tens and recognizing two-digit numbers with zero in the ones place are east to add.
Subtraction:
The standard algorithm for subtracting numbers that require regrouping can be difficult for children to master.
* Modeling the algorithmic process with manipulative such as base-ten blocks helps children to understand the regrouping process.
* If children are familiar with the term "borrowing" to describe the regrouping that takes place, modeling will help them see that regrouping, or trading, better describes the process.
* Explaining modes and recording what they show will strengthen children's conceptual and procedural understanding of 2-digit subtraction.
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