Illuminations: What Balances?
Illuminations (National Council of Teachers of Mathematics)

This lesson encourages students to explore another meaning of subtraction, the balance.

Illuminations: Commutative Rectangle
Illuminations (National Council of Teachers of Mathematics)

Students typically learn about the concepts of identity, inverse, commutativity, and associativity by exploring the four basic operations (+, –, ×, and ÷) with integers.

Illuminations: The Plus Sign and Triangle
Illuminations (National Council of Teachers of Mathematics)

Using a scheme similar to the one in the Rectangle lesson of this unit, students will further explore the concepts of identity, inverse, and commutative and associative properties.