Multiplication of mixed fractions occurs regularly in real-life situations.

For example, suppose that a country road is 5 \, \dfrac 12\,\textrm{km} long. If \dfrac 35 of it is paved with asphalt, how long is the paved part?

To find out the length of the paved part of the road, we need to calculate 5 \, \dfrac{1}{2} \times \dfrac{3}{5}.

First, we write 5 \,\dfrac{1}{2} as an improper fraction:

5 \,\dfrac{1}{2} = \dfrac{(5 \times 2) + 1}{2} = \dfrac{11}{2}

Now, we can multiply the two numbers. We multiply the numerators, and we multiply the denominators:

\dfrac{11}{2} \times \dfrac{3}{5} = \dfrac{11 \times 3}{2 \times 5} = \dfrac{33}{10}

Finally, by converting this fraction to a mixed number, we get

33 \div 10 = 3\,\textrm{R}\,3 = 3\,\dfrac{3}{10}.

So, the paved part of the road is 3\,\dfrac{3}{10}\,\textrm{km} long.

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Customers are served every 2\,\dfrac{1}{4} minutes at a particular bank. How long does it take to serve eight customers?

EXPLANATION

To find out how long it takes to serve eight customers, we need to multiply 2 \, \dfrac{1}{4} by 8.

First, we write 2\,\dfrac{1}{4} as an improper fraction: 2\,\dfrac{1}{4} = \dfrac{(2 \times 4) + 1}{4} = \dfrac{9}{4}

We also write 8 as an improper fraction: 8 = \dfrac{8}{1}

So now, we need to solve the following multiplication problem:

\dfrac{9}{\color{red}4} \times \dfrac{\color{blue}8}{1}.

Notice that the first fraction's denominator ( \color{red}4 ) and the second fraction's numerator ( \color{blue}8 ) have a common factor of 4.

Therefore, we can simplify our problem by swapping the denominators first and then multiplying the resulting fractions:

\begin{align*} \dfrac{9}{\color{red}4} \times \dfrac{\color{blue}8}{1} &= \dfrac{9}{1} \times \dfrac{\color{blue}8}{\color{red}4} \\[5pt] &= \dfrac{9}{1} \times 2 \\[5pt] &= 9 \times 2 \\[5pt] &= 18 \end{align*}

Therefore, it takes 18 minutes to serve 8 customers.

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Mary wants to make $5$ strawberry cakes. If she uses $1\dfrac{1}{3}\,\textrm{lb}$ of strawberries for each cake, how many strawberries does she need?

a
$6\,\dfrac{2}{3}\,\textrm{lb}$
b
$4\,\dfrac{2}{3}\,\textrm{lb}$
c
$5\,\dfrac{2}{3}\,\textrm{lb}$
d
$8\,\dfrac{1}{3}\,\textrm{lb}$
e
$7\,\dfrac{1}{3}\,\textrm{lb}$

Nancy uses $2 \dfrac{1}{4}$ cups of flour to make a dozen cupcakes. How many cups of flour does she need to prepare an order for $6$ dozen cupcakes?

a
$13\,\dfrac{1}{2}$ cups
b
$12\,\dfrac{1}{2}$ cups
c
$11\,\dfrac{1}{2}$ cups
d
$14\,\dfrac{1}{2}$ cups
e
$10\,\dfrac{1}{2}$ cups

A field has an area of 2 \, \dfrac{2}{3} acres. If a farmer wants to use \dfrac{3}{5} of the field to grow corn, how much of the field would be used to grow corn?

EXPLANATION

To find out the area used to grow corn, we need to calculate 2 \, \dfrac{2}{3} \times \dfrac{3}{5}.

First, we write 2 \,\dfrac{2}{3} as an improper fraction: 2 \,\dfrac{2}{3} = \dfrac{(2 \times 3) + 2}{3} = \dfrac{8}{3}

So now, we need to solve the following multiplication problem:

\dfrac{8}{\color{red}3} \times \dfrac{\color{blue}3}{5}

Notice that the first fraction's denominator ( \color{red}3 ) and the second fraction's numerator ( \color{blue}3 ) have a common factor of 3.

Therefore, we can simplify our problem by swapping the denominators first and then multiplying the resulting fractions:

\begin{align*} \dfrac{8}{\color{red}3} \times \dfrac{\color{blue}3}{5} &= \dfrac{8}{5} \times \dfrac{\color{blue}3}{\color{red}3} \\[5pt] &= \dfrac{8}{5} \times 1 \\[5pt] &=\dfrac{8}{5} \end{align*}

Finally, by converting this fraction to a mixed number, we get 8\div 5 = 1\,\textrm{R} \, 3 = 1\,\dfrac{3}{5} \, .

So, 1\,\dfrac{3}{5} acres would be used to grow corn.

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A box full of raisins weighs $3\, \dfrac 13\,\textrm{oz}.$ Alex took some out to eat, and now the box is only $\dfrac 23$ full. How much does the box weigh now?

a
$2\,\dfrac{2}{3}\,\textrm{oz}$
b
$2\,\dfrac{2}{9}\,\textrm{oz}$
c
$1\,\dfrac{1}{3}\,\textrm{oz}$
d
$3\,\dfrac{2}{9}\,\textrm{oz}$
e
$1\,\dfrac{2}{3}\,\textrm{oz}$

Fred is $4 \, \dfrac{1}{2}\,\textrm{ft}$ tall. Julie is $\dfrac{4}{5}$ of Fred's height. How tall is Julie?

a
$3\,\dfrac{2}{5}\,\textrm{ft}$
b
$3\,\textrm{ft}$
c
$3\,\dfrac{3}{5}\,\textrm{ft}$
d
$4\,\textrm{ft}$
e
$3\,\dfrac{4}{5}\,\textrm{ft}$

A chocolate bar is made with 1\, \dfrac{1}{4}\,\textrm{oz} of cocoa. If Casey has 2\, \dfrac{2}{3} bars, how many ounces of cocoa did it take to make them?

EXPLANATION

To find out how many ounces of cocoa it took to make the chocolate bars, we need to calculate 1 \, \dfrac{1}{4} \times 2 \, \dfrac{2}{3}.

First, we write 1\,\dfrac{1}{4} as an improper fraction: 1 \, \dfrac{1}{4} = \dfrac{(1 \times 4) + 1}{4}= \dfrac{5}{4}

We also write 2 \, \dfrac{2}{3} as an improper fraction: 2 \, \dfrac{2}{3}=\dfrac{(2 \times 3)+2}{3}= \dfrac{8}{3}

So now, we need to solve the following multiplication problem:

\dfrac{5}{\color{red}4} \times \dfrac{\color{blue}8}{3}

Notice that the first fraction's denominator ( \color{red}4 ) and the second fraction's numerator ( \color{blue}8 ) have a common factor of 4.

Therefore, we can simplify our problem by swapping the denominators first and then multiplying the resulting fractions:

\begin{align*} \dfrac{5}{\color{red}4} \times \dfrac{\color{blue}8}{3} &= \dfrac{5}{3} \times \dfrac{\color{blue}8}{\color{red}4} \\[5pt] &= \dfrac{5}{3} \times \dfrac{2}{1} \\[5pt] &= \dfrac{5 \times 2}{3 \times 1} \\[5pt] &=\dfrac{10}{3} \end{align*}

Finally, we write the resulting improper fraction as a mixed number: \dfrac{10}{3} =3\,\textrm{R}\, 1 = 3 \, \dfrac{1}{3}

So, it took 3 \, \dfrac{1}{3}\,\textrm{oz} of cocoa to make Casey's chocolate bars.

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A box of cornflakes cereal weighs $1\dfrac 12\,\textrm{oz}.$ Last week, Debby ate $2$ full boxes and another box which was only $\dfrac 14$ full. How many ounces of this cereal did Debbie eat in total?

a
$3 \, \dfrac{1}{8}\,\textrm{oz}$
b
$2 \, \dfrac{5}{8}\,\textrm{oz}$
c
$3 \, \dfrac{3}{8}\,\textrm{oz}$
d
$2 \, \dfrac{7}{8}\,\textrm{oz}$
e
$2 \, \dfrac{1}{8}\,\textrm{oz}$

Terry had a lump of play-doh that was $1 \,\dfrac 13\,\textrm{in}$ long. How long would it be if Terry stretches it out to $1 \, \dfrac 18$ times its original length?

a
$1 \, \dfrac{1}{2}\,\textrm{in}$
b
$2 \, \dfrac{1}{8}\,\textrm{in}$
c
$1 \, \dfrac{3}{8}\,\textrm{in}$
d
$1 \, \dfrac{3}{4}\,\textrm{in}$
e
$2 \, \dfrac{5}{8}\,\textrm{in}$
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