We can use multiplication as repeated addition and the relationship between multiplication and division to solve division problems.

For example, suppose we are given the following multiplication problem:

20 \times 4 = {\color{blue}{80}}

As we've seen, we can generate more multiplication problems using repeated addition. For example:

\begin{align*} 21 \times 4 &= {\color{blue}{80}} + 4 = {\color{red}{84}} \\[10pt] 22 \times 4 &= {\color{red}{84}} + 4 = {\color{purple}{88}} \end{align*}

Let's write these results a little more clearly (without the intermediate step):

\begin{align*} 21 \times 4 &= {\color{red}{84}} \\[10pt] 22 \times 4 &= {\color{purple}{88}} \end{align*}

Each of these new multiplication problems can be used to generate two new division problems!

\begin{align*} {\color{red}{84}} &\div 4 = 21, \qquad &&{\color{red}{84}} \div 21 = 4 \\[10pt] {\color{purple}{88}}&\div 4 = 22, \qquad &&{\color{purple}{88}}\div 22 = 4 \end{align*}

We can use this idea to help us divide large numbers. Let's see how.

FLAG

You're given the following multiplication problem: 10 \times 7 = 70 Use the equation above and the relationship between multiplication and division to determine which of the following is the solution to 98 \div 7.

  1. 11
  2. 12
  3. 13
  4. 14
EXPLANATION

If 98 \div 7 = \fbox{[math]\phantom{0}[/math]}, then by the relationship between multiplication and division, we have \fbox{[math]\phantom{0}[/math]} \times 7 = 98.

We start with the given multiplication problem: 10 \times 7 = {\color{blue}{70}}

Let's now try the numbers in the list, starting with the smallest. We can use repeated addition to compute the products. \begin{align*} 11 \times 7 & = {\color{blue}{70}} + 7 = {\color{red}{77}}\qquad{\color{red}{\times}} \\[10pt] 12 \times 7 & = {\color{red}{77}} + 7 = {\color{purple}{84}} \qquad{\color{red}{\times}} \\[10pt] 13 \times 7 &= {\color{purple}{84}} + 7 = {\color{magenta}91} \qquad{\color{red}{\times}} \\[10pt] 14 \times 7 &= {\color{magenta}{91}} + 7 = 98 \qquad{\color{green}{\checkmark}} \end{align*}

Therefore, 98 \div 7 = 14.

FLAG

You're given the following multiplication problem:

\[ 30\times 3 = 90 \]

Use the equation above and the relationship between multiplication and division to find the solution to $96 \div 3.$

a
$35$
b
$33$
c
$32$
d
$34$
e
$31$

You're given the following multiplication problem: \[ 40 \times 2 = 80 \] Use the equation above and the relationship between multiplication and division to find the solution to $86 \div 2.$

a
$43$
b
$41$
c
$44$
d
$45$
e
$42$

You're given the following multiplication problem: 120 \times 4 = 480 Use the equation above and the relationship between multiplication and division to find which of the following is the solution to 488 \div 4.

  1. 121
  2. 122
  3. 123
  4. 124
EXPLANATION

If 488 \div 4 = \fbox{[math]\phantom{0}[/math]}, then by the relationship between multiplication and division, we have \fbox{[math]\phantom{0}[/math]} \times 4 = 488.

We start with the given multiplication problem: 120 \times 4 = {\color{blue}{480}}

Let's try the numbers in the list, starting with the smallest. We can use repeated addition to compute the products. \begin{align*} 121 \times 4 & = {\color{blue}{480}} + 4 = {\color{red}{484}}\qquad{\color{red}{\times}} \\[10pt] 122 \times 4 & = {\color{red}{484}} + 4 = 488 \qquad{\color{green}{\checkmark}} \end{align*}

Therefore, 488 \div 4 = 122.

FLAG

You're given the following multiplication problem:

\[ 30\times 6 = 180 \]

Use the equation above and the relationship between multiplication and division to find the solution to $198 \div 6.$

a
$32$
b
$31$
c
$33$
d
$35$
e
$34$

You're given the following multiplication problem:

\[ 120\times 5 = 600 \]

Use the equation above and the relationship between multiplication and division to find the solution to $615 \div 5.$

a
$122$
b
$125$
c
$123$
d
$124$
e
$120$

We can also use repeated subtraction and the relationship between multiplication and division to solve division problems.

We once again consider the following multiplication problem:

20 \times 4 = {\color{blue}{80}}

Let's generate some more multiplication problems using repeated subtraction:

\begin{align*} 19 \times 4 &= {\color{blue}{80}} - 4 = {\color{red}{76}} \\[10pt] 18 \times 4 &= {\color{red}{76}} - 4 = {\color{purple}{72}} \end{align*}

Writing these results a little more clearly (without the intermediate step), we get the following:

\begin{align*} 19 \times 4 &= {\color{red}{76}} \\[10pt] 18 \times 4 &= {\color{purple}{72}} \end{align*}

Each of these new multiplication problems can be used to generate two new division problems:

\begin{align*} {\color{red}{76}} &\div 4 = 19, \qquad &&{\color{red}{76}} \div 19 = 4 \\[10pt] {\color{purple}{72}}&\div 4 = 18, \qquad &&{\color{purple}{72}}\div 18 = 4 \end{align*}

Let's now use repeated subtraction to help us divide some large numbers.

FLAG

You're given the following multiplication problem: 70 \times 4 = 280 Use the equation above and the relationship between multiplication and division to find which of the following is the solution to 268 \div 4.

  1. 69
  2. 68
  3. 67
  4. 66
EXPLANATION

If 268 \div 4 = \fbox{[math]\phantom{0}[/math]}, then by the relationship between multiplication and division, we have \fbox{[math]\phantom{0}[/math]} \times 4 = 268.

We start with the given multiplication problem: 70 \times 4 = {\color{blue}{280}}

Let's now try the numbers in the list, starting with the largest. We can use repeated subtraction to compute the products. \begin{align*} 69 \times 4 & = {\color{blue}{280}} - 4 = {\color{red}{276}}\qquad{\color{red}{\times}} \\[10pt] 68 \times 4 &= {\color{red}{276}} - 4 = {\color{purple} 272}\qquad{\color{red}{\times}} \\[10pt] 67 \times 4 &= {\color{purple}{272}} - 4 = 268 \qquad{\color{green}{\checkmark}} \end{align*}

Therefore, 268 \div 4 = 67.

FLAG

You're given the following multiplication problem:

\[ 30\times 3 = 90 \]

Use the equation above and the relationship between multiplication and division to find the solution to $84 \div 3.$

a
$27$
b
$28$
c
$25$
d
$29$
e
$26$

You're given the following multiplication problem: \[ 40 \times 9 = 360 \] Use the equation above and the relationship between multiplication and division to find the solution to $324 \div 9.$

a
$36$
b
$37$
c
$38$
d
$35$
e
$39$
Flag Content
Did you notice an error, or do you simply believe that something could be improved? Please explain below.
SUBMIT
CANCEL