# Module 2

### Introduction to Place Value Through Addition and Subtraction within 20

## Standards

1.OA.A.1: Use addition and subtraction within 20 to solve word problems involving situations of adding to, taking from, putting together, taking apart, and comparing, with unknowns in all positions, e.g., by using objects, drawings, and equations with a symbol for the unknown number to represent the problem.

- I can use a symbol (e.g. ?, x) to represent an unknown number in a problem.
- I can determine the operation to solve word problems with unknowns.
- I can solve word problems by adding 3 numbers in different ways.

1.OA.B.3: Apply properties of operations as strategies to add and subtract. Examples: If 8 + 3 = 11 is known, then 3 + 8 = 11 is also known. (Commutative property of addition.) To add 2 + 6 + 4, the second two numbers can be added to make a ten, so 2 + 6 + 4 = 2 + 10 = 12. (Associative property of addition.)

- I can explain how properties of addition and subtraction work.
- I can use strategies to solve addition and subtraction problems.

1.OA.B.4: Understand subtraction as an unknown-addend problem. For example, subtract 10 – 8 by finding the number that makes 10 when added to 8.

- I can identify the unknown in a subtraction problem.
- I can solve subtraction problems to find the missing addend.
- I can explain the relationship of addition and subtraction.

1.OA.C.6: Add and subtract within 20, demonstrating fluency for addition and subtraction within 10. Use strategies such as counting on; making ten (e.g., 8 + 6 = 8 + 2 + 4 = 10 + 4 = 14); decomposing a number leading to a ten (e.g., 13 – 4 =13 – 3 – 1 = 10 – 1 = 9); using the relationship between addition and subtraction (e.g., knowing that 8 + 4 = 12, one knows 12 – 8 = 4); and creating equivalent but easier or known sums (e.g., adding 6 + 7 by creating the known equivalent 6 + 6 + 1 = 12 + 1 = 13).

- I can add within 20.
- I can subtract within 20.
- I can use strategies to add and subtract within 20.
- I can add fluently within 10.
- I can subtract fluently within 10

1.NBT.B.2: Understand that the two digits of a two-digit number represent amounts of tens and ones. Understand the following as special cases:

1.NBT.B.2a: 10 can be thought of as a bundle of ten ones—called a “ten.”

1.NBT.B.2b: The numbers from 11 to 19 are composed of a ten and one, two, three, four, five, six, seven, eight, or nine ones.

1.NBT.B.2c: The numbers 10, 20, 30, 40, 50, 60, 70, 80, 90 refer to one, two, three, four, five, six, seven, eight, or nine tens (and 0 ones).

- I can explain what each digit of a two-digit number represents.
- I can identify a bundle of 10 ones as a “ten”.
- I can represent numbers 11 to 19 as a 10 and ones.
- I can represent numbers 20 to 90 as tens and zero ones.