Lesson 7: Multiply Mixed Numbers

Property

The area model is a visual representation of the distributive property for multiplying mixed numbers. Each partial product in the area model corresponds to a term in the expanded form of the multiplication. For $W_1 \frac{n_1}{d_1} \times W_2 \frac{n_2}{d_2}$:

Examples

• To multiply $2 \frac{1}{2} \times 1 \frac{1}{4}$, we can write it as $(2 + \frac{1}{2}) \times (1 + \frac{1}{4})$. The four partial products in the area model correspond to the terms from the distributive property:
• $2 \times 1 = 2$
• $2 \times \frac{1}{4} = \frac{2}{4}$
• $\frac{1}{2} \times 1 = \frac{1}{2}$
• $\frac{1}{2} \times \frac{1}{4} = \frac{1}{8}$
• For $3 \frac{2}{3} \times 4 \frac{1}{2} = (3 + \frac{2}{3}) \times (4 + \frac{1}{2})$, the partial products are:
• $3 \times 4 = 12$
• $3 \times \frac{1}{2} = \frac{3}{2}$
• $\frac{2}{3} \times 4 = \frac{8}{3}$
• $\frac{2}{3} \times \frac{1}{2} = \frac{2}{6}$

Explanation

This method connects the visual area model with the algebraic distributive property. By breaking each mixed number into its whole number and fraction parts, you create four multiplication problems. The sum of these four "partial products" gives you the final answer. This helps to understand why the area model works and reinforces the concept of distribution.

Property

To multiply mixed numbers, follow these steps:

1. Convert: Change each mixed number into an improper fraction using the formula $a\frac{b}{c} = \frac{(a \times c) + b}{c}$.
2. Multiply: Multiply the numerators, and multiply the denominators.
3. Simplify: Simplify the resulting fraction and convert it back to a mixed number if needed.

Examples