Let's think about how to simplify the following: \dfrac{\left(\dfrac{2}{3}\right)}{\left(\dfrac{3}{4}\right)}

The expression above is a fraction, but there are additional fractions in the numerator and denominator. Such expressions are called fractions of fractions. We use parentheses to make it easier to read.

The trick to working with fractions of fractions is to remember that a fraction represents a division. So, a fraction of fractions is a division of two fractions: \dfrac{\left(\dfrac{2}{3}\right)}{\left(\dfrac{\color{blue}{3}}{\color{red}{4}}\right)} = \left(\dfrac{2}{3}\right) \boldsymbol{\div} \left(\dfrac{\color{blue}{3}}{\color{red}{4}}\right)

Now, recall that dividing by \dfrac{\color{blue}{3}}{\color{red}{4}} is the same as multiplying by its reciprocal \dfrac{\color{red}{4}}{\color{blue}{3}}. We can use this fact to simplify the fraction above:

\begin{align*} \left(\dfrac{2}{3}\right) \boldsymbol{\div} \left(\dfrac{\color{blue}{3}}{\color{red}{4}}\right) &=\\[5pt] \left(\dfrac{2}{3}\right) \boldsymbol{\times} \left(\dfrac{\color{red}{4}}{\color{blue}{3}}\right) &=\\[5pt] \dfrac{2\times 4}{3\times 3} &=\\[5pt] \dfrac{8}{9}& \end{align*}

Therefore,

\dfrac{\left(\dfrac{2}{3}\right)}{\left(\dfrac{3}{4}\right)} = \dfrac{8}{9}.

FLAG

What is \dfrac {\left(\dfrac 1 4\right)} {\left(-\dfrac 3 7\right)} expressed as a single fraction?

EXPLANATION

First, remember that a fraction represents a division. So, a fraction of fractions is a division of two fractions:

\begin{align} \dfrac {\left(\dfrac 1 4\right)} {\left(-\dfrac 3 7\right)} &= \dfrac 1 4 \div \left(-\dfrac 3 7\right) \end{align}

Now, recall that dividing by -\dfrac{3}{7} is the same as multiplying by its reciprocal -\dfrac{7}{3}. We can use this fact to simplify the fraction above:

\begin{align} \dfrac 1 4 \div \left(-\dfrac 3 7\right) &=\\[5pt] \dfrac 1 4 \times \left(-\dfrac 7 3\right) &=\\[5pt] -\dfrac {1 \times 7} {4\times 3} &=\\[5pt] -\dfrac {7} {12} & \end{align}

Therefore,

\begin{align} \dfrac {\left(\dfrac 1 4\right)} {\left(-\dfrac 3 7\right)} &= -\dfrac {7} {12} . \end{align}

Notice that we used the fact that a positive number times a negative number gives a negative number.

FLAG

$\dfrac{\left( \dfrac{2}{5} \right)}{\left( \dfrac{8}{5} \right)}=$

a
$\dfrac{2}{3}$
b
$\dfrac{3}{4}$
c
$\dfrac{1}{4}$
d
$\dfrac{4}{5}$
e
$\dfrac{2}{7}$

$\dfrac{\left(-\dfrac{3}{2}\right)}{\left(\dfrac{2}{5}\right)}=$

a
$-\dfrac{10}{3}$
b
$-\dfrac{15}{4}$
c
$-\dfrac{6}{5}$
d
$-\dfrac 2 3$
e
$-5$

$\dfrac{\:\left(-\dfrac{6}{15}\right)\:}{\left(-\dfrac{12}{9}\right)}=$

a
$\dfrac{3}{10}$
b
$\dfrac{4}{7}$
c
$9$
d
$\dfrac{1}{4}$
e
$\dfrac{3}{5}$

How do we simplify \dfrac{5}{\left(\dfrac{2}{3}\right)}? Notice that, this time, we have a counting number divided by a fraction.

The trick is to write 5 = \dfrac{\color{blue}{5}}{\color{red}{1}} and perform the same process as before:

\begin{align} \dfrac{5}{\left(\dfrac{2}{3}\right)} &=\\[5pt] 5 \div \left(\dfrac{2}{3}\right) &=\\[5pt] \left( \dfrac{\color{blue}{5}}{\color{red}{1}} \right) \div \left(\dfrac{2}{3}\right) &=\\[5pt] \left(\dfrac 5 1\right) \times \left(\dfrac{3}{2}\right) &=\\[5pt] \dfrac{5\times 3}{1\times 2} &=\\[5pt] \dfrac{15}{2}& \end{align}

FLAG

Simplify \dfrac{\left(-3\right)} {\left(-\dfrac 3 5\right)}.

EXPLANATION

First, remember that a fraction represents a division:

\begin{align} \dfrac{\left(-3\right)} {\left(-\dfrac 3 5\right)}= -3 \div \left(-\dfrac 35\right) \end{align}

Now, recall that -3 =- \dfrac{3}{1} and dividing by -\dfrac{3}{5} is the same as multiplying by its reciprocal -\dfrac{5}{3}. We can use these facts to simplify the fraction above:

\begin{align} % \dfrac {\left(-3\right)}{\left(-\dfrac 3 5\right)} &=\\[5pt] (-3) \div \left(-\dfrac 3 5\right) &=\\[5pt] \left(-\dfrac 3 1\right) \div \left(-\dfrac 3 5\right) &= \\[5pt] \left(-\dfrac 3 1\right) \times \left(-\dfrac 5 3\right) &=\\[5pt] \dfrac{3\times 5}{1\times 3} &=\\[5pt] \dfrac{15}{3} &=\\[5pt] 5& \end{align}

Therefore,

\dfrac{\left(-3\right)} {\left(-\dfrac 3 5\right)} = 5.

Notice that we used the fact that a negative number times a negative number gives a positive number.

FLAG

$\dfrac{3} {\left(\dfrac 7 3 \right)}=$

a
$\dfrac{9}{7}$
b
$\dfrac{7}{9}$
c
$7$
d
$\dfrac{3}{7}$
e
$\dfrac{7}{3}$

$\dfrac{7} {\left(-\dfrac 1 2 \right)}=$

a
$-14$
b
$-\dfrac{1}{14}$
c
$-\dfrac{1}{7}$
d
$-\dfrac{7}{2}$
e
$-\dfrac{2}{7}$

$\dfrac{\:\:(-9)\:\:}{\left(\dfrac{1}{2}\right)}=$

a
$-81$
b
$-4\dfrac{1}{2}$
c
$18$
d
$4\dfrac{1}{2}$
e
$-18$

Suppose we want to simplify a fraction of fractions like \dfrac{\left(\dfrac{5}{3}\right)}{4}. In this case, we have a fraction divided by a counting number. We have two methods available.

The long way is to write 4 = \dfrac 4 1 and then calculate in the same way as we did earlier:

\begin{align} \dfrac{\left(\dfrac{5}{3}\right)}{4} &=\\[5pt] \left(\dfrac{5}{3}\right) \div 4 &=\\[5pt] \left(\dfrac{5}{3}\right) \div \left(\frac 4 1\right) &=\\[5pt] \left(\dfrac{5}{3}\right) \times \left(\frac 1 4\right) &=\\[5pt] \dfrac{5\times 1}{3\times 4} &=\\[5pt] \dfrac{5}{12}& \end{align}

A quicker way is to recognize that the result will have the same numerator as the top fraction and that the denominator is just the product of the two denominators:

\begin{align} \dfrac{\left(\dfrac{5}{3}\right)}{\color{blue}{4}} =\dfrac{5}{3\times \color{blue}{4}} =\dfrac{5}{12} \end{align}

FLAG

Calculate \dfrac{\left(-\dfrac 3 2\right)}{6}.

EXPLANATION

We can use either of the following two methods.

Method 1 - The Long Way

First, remember that a fraction represents a division:

\dfrac{\left(-\dfrac 3 2\right)}{6} = \left(-\dfrac 3 2\right) \div 6

Now, recall that dividing by 6 is the same as multiplying by its reciprocal \dfrac{1}{6}. We can use this fact to simplify the fraction above:

\begin{align} \require{cancel} \left(-\dfrac{3}{2}\right) \div 6 &=\\[5pt] \left(-\dfrac{3}{2}\right) \times \left(\frac 1 6\right) &=\\[5pt] - \dfrac{3\times 1}{2\times 6} &=\\[5pt] - \dfrac{3}{12} \end{align}

Finally, we simplify:

- \dfrac{3}{12} = - \dfrac{3 \div 3}{12 \div 3} = -\dfrac{1}{4}

Therefore, \dfrac{\left(-\dfrac 3 2\right)}{6}= -\dfrac14

Method 2 - The Quick Way

The result will have the same numerator as the top fraction, and the denominator is just the product of the two denominators:

\begin{align} \dfrac{\left(-\dfrac 3 2\right)}{6} &=\\[5pt] \dfrac{-3}{2\times 6} &=\\[5pt] -\dfrac{3}{12} &=\\[5pt] -\dfrac{3 \div 3}{12 \div 3} &=\\[5pt] -\dfrac{1}{4}& \end{align}

FLAG

$\dfrac{\left(\dfrac 8 5 \right)}{2}=$

a
$\dfrac{16}{5}$
b
$\dfrac{5}{16}$
c
$\dfrac{4}{5}$
d
$5$
e
$\dfrac{2}{5}$

$\dfrac{\left(- \dfrac 7 2 \right)}{5}=$

a
$-\dfrac{14}{5}$
b
$-\dfrac{7}{10}$
c
$0.7$
d
$\dfrac{7}{5}$
e
$-\dfrac{5}{14}$

$\dfrac{\left(-\dfrac 2 5 \right)}{(-5)}=$

a
$\dfrac{1}{5}$
b
$-\dfrac{1}{10}$
c
$\dfrac{5}{2}$
d
$\dfrac{2}{25}$
e
$-2$
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