Learning Outcomes
- Multiply and divide mixed numbers
In the previous section, you learned how to multiply fractions and how to divide fractions. All of the examples there used either proper or improper fractions. What happens when you are asked to multiply or divide mixed numbers? Remember that we can convert a mixed number to an improper fraction.
Example
Multiply: [latex]3\Large\frac{1}{3}\cdot \frac{5}{8}[/latex]
Solution:
[latex]3\Large\frac{1}{3}\cdot \frac{5}{8}[/latex] | |
Convert [latex]\Large3\frac{1}{3}[/latex] to an improper fraction. | [latex]\Large\frac{10}{3}\cdot \frac{5}{8}[/latex] |
Multiply. | [latex]\Large\frac{10\cdot 5}{3\cdot 8}[/latex] |
Look for common factors. | [latex]\Large\frac{\color{red}{2}\cdot 5\cdot 5}{3\cdot \color{red}{2} \cdot 4}[/latex] |
Remove common factors. | [latex]\Large\frac{5\cdot 5}{3\cdot 4}[/latex] |
Simplify. | [latex]\Large\frac{25}{12}[/latex] |
Notice that we left the answer as an improper fraction, [latex]\Large\frac{25}{12}[/latex], and did not convert it to a mixed number. In algebra, it is preferable to write answers as improper fractions instead of mixed numbers. This avoids any possible confusion between [latex]2\Large\frac{1}{12}[/latex] and [latex]2\cdot\Large\frac{1}{12}[/latex] (which are not equal!).
Try it
Watch the following video for another example of how to multiply a mixed number by a fraction.
Multiply or divide mixed numbers
- Convert the mixed numbers to improper fractions.
- Follow the rules for fraction multiplication or division.
- Simplify if possible.
Example
Multiply, and write your answer in simplified form: [latex]2\Large\frac{4}{5}\left(\normalsize -1\Large\frac{7}{8}\right)[/latex]
Try It
In the following video we show more examples of how to multiply mixed numbers that are negative.
Example
Divide, and write your answer in simplified form: [latex]3\Large\frac{4}{7}\normalsize\div 5[/latex]
Try It
Example
Divide: [latex]2\Large\frac{1}{2}\normalsize\div 1\Large\frac{1}{4}[/latex]
Try It
The next video provides several more examples of dividing mixed numbers, whole numbers and fractions.