Suppose that we want to solve the equation \dfrac{2}{3}x = 8.

This equation has a fractional coefficient of \dfrac{2}{3}. The term \dfrac{2}{3}x means that x is being multiplied by 2 and divided by 3.

We can solve this problem by applying the multiplication principle, twice. First, we multiply both sides by {\color{blue}{3}} to get rid of the fraction:

\eqalign{ \dfrac{2}{3}x &= 8 \\[5pt] {\color{blue}{3}}\cdot \dfrac{2}{3}x &={\color{blue}{3}}\cdot 8 \\[5pt] \cancel{\color{blue}{3}} \cdot \dfrac{2}{\cancel{3}}x &={\color{blue}{3}}\cdot 8 \\ 2x &=24 }

Then, we divide both sides by {\color{red}{2}} to isolate x\mathbin{:}

\eqalign{ 2x &=24\\[5pt] \dfrac{2x}{{\color{red}{2}}} &=\dfrac{24}{{\color{red}{2}}} \\[5pt] \dfrac{\cancel{2}x}{\cancel{\color{red}{2}}} &=\dfrac{24}{{\color{red}{2}}} \\ x &=12 }

FLAG

Solve for x, if -\dfrac{3}{4}x = 12.

EXPLANATION

First, we multiply both sides by \color{blue}4 to get rid of the fraction:

\begin{align*} \require{cancel} -\dfrac{3}{4}x &= 12 \\[5pt] {\color{blue}4} \cdot \left( -\dfrac{3}{4}x \right) &= {\color{blue}4} \cdot 12 \\[5pt] \cancel{\color{blue}4} \cdot \left( - \dfrac{3}{\cancel{4}}x \right) &= 48 \\[5pt] -3x &= 48 \end{align*}

Then, we divide both sides of the equation by {\color{red}-3} to isolate x\mathbin{:}

\begin{align*} -3x &= 48 \\[5pt] \dfrac{-3x}{{\color{red}-3}} &= \dfrac{48}{{\color{red}-3}} \\[5pt] \dfrac{\cancel{-3}x}{\cancel{\color{red}-3}} &= -16 \\ x &= -16 \end{align*}

FLAG

If $\dfrac 4 3 x = 8$, then $x =$

a
$3$
b
$6$
c
$\dfrac{3}{32}$
d
$\dfrac{1}{6}$
e
$\dfrac{32}{3}$

If $\dfrac 2 5 x = 4$, then $x =$

a
$10$
b
$18$
c
$\dfrac 5 8$
d
$\dfrac 3 7$
e
$\dfrac 8 5$

When solving equations with fractional coefficients, there is a shortcut! We can complete division and multiplication in a single step by multiplying both sides of the equation by the reciprocal of the fractional coefficient.

For example, to solve the equation \dfrac{2x}{5}= 6, we first express the fraction as a coefficient:

\require{cancel} \eqalign{ \dfrac{2}{5}x &= 6 }

The fractional coefficient is \dfrac{2}{5} , and its reciprocal is \left(\dfrac 2 5\right)^{-1} = {\color{blue}{\dfrac 5 2}}. Because the product of a fraction and its reciprocal is equal to 1, we can multiply both sides of the equation by the reciprocal to isolate x\mathbin{:}

\require{cancel} \eqalign{ \dfrac{2}{5}x &= 6 \\[5pt] \underbrace{ {\color{blue}{\dfrac 5 2}} \cdot \dfrac{2}{5} }_{\large =\, 1} x &= {\color{blue}{\dfrac 5 2}} \cdot 6 \\[5pt] 1 x &= \dfrac{5\cdot 6}{2} \\[5pt] x &= \dfrac{30}{2} \\[5pt] x &= 15 }

FLAG

If -\dfrac{3}{2}t = 24 , then what is the value of t?

EXPLANATION

We multiply both sides of the equation by the reciprocal of -\dfrac{3}{2}, which is \left( -\dfrac{3}{2} \right)^{-1} = -\dfrac{2}{3}. This gives \begin{eqnarray} \require {cancel} \eqalign{ -\dfrac{3}{2}t &= 24 \\[5pt] -\dfrac{2}{3} \cdot \left(-\dfrac{3}{2}t \right) &= -\dfrac{2}{3} \cdot 24 \\[5pt] 1t &= -\dfrac{2}{ \cancel{3} } \cdot \cancel{3} \cdot 8 \\[5pt] t &= -16. } \end{eqnarray}

FLAG

If $-\dfrac{12}{5}v = 7,$ then $v=$

a
$-\dfrac{35}{12}$
b
$-\dfrac{57}{12}$
c
$-\dfrac{84}{5}$
d
$-\dfrac{75}{12}$
e
$-\dfrac{7}{5}$

If $\dfrac{7w}{17}=-7$, then $w =$

a
$-7$
b
$-\dfrac{17}{7}$
c
$17$
d
$-17$
e
$-\dfrac{7}{17}$

Solve the equation \dfrac{3x}{4}-5 = -8.

EXPLANATION

First, we isolate the fractional term \dfrac{3x}{4} by adding 5 to both sides:

\eqalign{ \dfrac{3x}{4}-5 &=-8\\[5pt] \dfrac{3x}{4}-5+5 &=-8+5\\[5pt] \dfrac{3x}{4}+0 &=-3 \\[5pt] \dfrac{3x}{4} &=-3 }

The fractional coefficient is \dfrac{3}{4}, so we multiply by its reciprocal \left( \dfrac{3}{4} \right)^{-1} = \dfrac{4}{3}. This gives

\eqalign{ \dfrac{3}{4}x &=-3 \\[5pt] \dfrac{4}{3} \cdot \dfrac{3}{4}x &= \dfrac{4}{3} \cdot (-3) \\[5pt] 1 x &= - \dfrac{4}{\cancel{3} } \cdot \cancel{3} \\[5pt] x &= -4. }

FLAG

If $\dfrac {5z} 3 + \dfrac 1 2= 1$, then $z =$

a
$\dfrac 6 {10} $
b
$3$
c
$\dfrac 3 {10} $
d
$\dfrac 9 2 $
e
$2$

If $\dfrac {7y} 2- 3 = 11$, then $y =$

a
$14$
b
$7$
c
$4$
d
$\dfrac {16} {7}$
e
$\dfrac {22} {7}$
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