Materials Needed: None

## WhyEdit

What does addition of fractions have in common with addition of decimals? What do these have in common with addition of expressions that contain variables? What does finding a perimeter have in common with balancing your checkbook?

## Learning ObjectivesEdit

- Explain why when we add, we need common denominators or like place values or like terms or common units.
- Solve problems that involve finding totals, finding perimeters, or combining values.
- Use the commutative property of addition to aid in performing mental addition.

## Warm-upEdit

An child in elementary is asked, "What is the value of 3 dimes and 5 pennies?" The child answers, "3 + 5 = 8. The money is worth 8 cents." Explain to the child why his reasoning is wrong, and how he could find the correct answer.

You can't add dimes and pennies because they have different values.

A correct way to add would be to convert the 3 dimes to 30 cents, and then to add the 8 pennies. The answer would be 38 cents.