Fractions

Multiplication and Division

 

Multiplying Fractions

 

\(\large \dfrac{\text{a}}{\text{b}}\times \dfrac{\text{c}}{\text{d}} = \dfrac{\text{a} \times \text{c}}{\text{b} \times \text{d}}\)

 

Example:

Evaluate  \(5\dfrac{2}{3} \times 2\dfrac{2}{17}\)

\begin{equation*} \begin{split} 5\dfrac{2}{3} \times 2\dfrac{2}{17}& = 5\frac{2}{3} \times 2\frac{2}{17}\:\:\:\:\:\color {blue}\text{change into improper fraction}\\\\ 5\dfrac{2}{3} \times 2\dfrac{2}{17}& = \left(\frac{15}{3} + \frac{2}{3}\right) \times \left(\frac{34}{17} + \frac{2}{17}\right)\\\\ 5\dfrac{2}{3} \times 2\dfrac{2}{17}& = \frac{17}{3} \times \frac{36}{17}\\\\ 5\dfrac{2}{3} \times 2\dfrac{2}{17}& =  \frac{17 \times 36}{3 \times 17}\:\:\:\:\color{blue}\text{multiply the numerators and multiply the denominators}\\\\ 5\dfrac{2}{3} \times 2\dfrac{2}{17}& = \frac{\cancel {17} \times \cancelto {12}{36}}{\cancelto {1}{3} \times \cancel {17}}\:\:\:\:\:\color {blue} \text{simplify}\\\\ 5\dfrac{2}{3} \times 2\dfrac{2}{17}& = 12 \end{split} \end{equation*}

Dividing Fractions

 

\(\large \dfrac{\text{a}}{\text{b}}\div \dfrac{\text{c}}{\text{d}} = \dfrac{\text{a}}{\text{b}}\times\dfrac{\text{d}}{\text{c}}\)

 

Example:

Evaluate  \(3\dfrac{3}{4} \div \dfrac{5}{8}\)

\begin{equation*} \begin{split} 3\dfrac{3}{4} \div \dfrac{5}{8}& =  \left(\frac{12}{4} + \frac{3}{4}\right) \div \frac{5}{8}\:\:\:\:\:\color {blue}\text{change into improper fraction}\\\\ 3\dfrac{3}{4} \div \dfrac{5}{8}& =  \frac{15}{4} \times \color{red} \frac{8}{5}\:\:\:\:\:\color{blue} \text{turn the second fraction upside down}\\\\ 3\dfrac{3}{4} \div \dfrac{5}{8}& =  \frac{\cancelto {3}{15} \times \cancelto {2}{8}}{\cancelto {1}{4} \times \cancelto {1}{5}}\\\\ 3\dfrac{3}{4} \div \dfrac{5}{8}& =  6 \end{split} \end{equation*}

 

Exercise

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