Math: More Addition and Subtraction Within 20

 Addition problem investigations require students to add two or three numbers, with a total within 20. They start with problems in which two of the numbers make a ten (for example, 6+8+4$6+8+4$) and learn that they can add numbers in any order, which can make adding easier. They discover the usefulness of grouping numbers to find a sum of 10 when adding. Students find the sum of two addends, using methods by which they count on or use related facts they know.

For example, making a ten is helpful when finding the value of 9+5$9+5$. Students can take 1 from the 5 and group it with the 9 to make 10, and then add the 4.

Subtraction problem investigations require students to use the relationship between additon and subtraction and their understanding of the usefulness of a ten.

For example, if given 15 - 8, students may take away 5 to get to 10 and then take away 3 to find the difference of 7. 

They also may start with 8 and count on by 2 to get to 10, and then add 5 to reach 15. They see that the difference is 7.