# Prealgebra for Two-Year Colleges/Workbook AIE/Properties of addition

Materials Needed: None

## Why

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 Objectives

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

## Warm-up

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.

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