**Click here for the Spanish Version:** **https://youtu.be/fjfMddTbwFo**

**In This Unit of Study…**

Students use and explain a variety of counting strategies, and they reason about the sums and differences of basic facts through sums of 20. After using one-to-one correspondence to count a set of items, students begin to find more efficient methods for counting. Students relate the concept of counting on to addition and of counting back to subtraction. The ability to add and subtract within 20 translates to being able to find the sum of 3 whole numbers. Students represent problems by using objects, drawings, and equations with a symbol for the unknown value in all positions, while understanding that the sum or difference can be on either side of the equal sign.

**B.E.S.T. Benchmarks:**

- MA.1.NSO.2.2 Add two whole numbers with sums from 0 to 20 and subtract using related facts with procedural reliability. (only within 10)
- MA.1.AR.1.1 Apply properties of addition to find a sum of three or more whole numbers. (only within 10)
- MA.1.AR.1.2 Solve addition and subtraction real-world problems using objects, drawings, or equations to represent the problem.
- MA.1.AR.2.1 Restate a subtraction problem as a missing addend problem using the relationship between addition and subtraction.
- MA.1.AR.2.3 Determine the unknown whole number in an addition or subtraction equation, relating three whole numbers, with the unknown in any position.

**Key Concepts:**

- I can add two whole numbers within 20 involving situations of adding to or putting together.
- I can subtract two whole numbers within 20 involving taking from or comparing using related addition facts.
- I can apply properties of addition by grouping certain numbers together when I have three whole numbers whose sum is less than or equal to 20.
- I can find an unknown whole number in an addition equation of three whole numbers whose sum is within 20 with a symbol for the unknown number in any position.
- I can find an unknown whole number in a subtraction equation of three whole numbers whose sum is within 20 with a symbol for the unknown number in any position.
- I can use the relationship between addition and subtraction to restate a subtraction problem as a missing addend problem to sums within 20.