To solve an equation with a decimal coefficient, such as 0.2x = -1,

we start by getting rid of the decimal. To do this, we multiply both sides of the equation by {\color{blue}10}. Multiplying a decimal by 10 shifts the decimal place one spot over to the right.

\begin{align} 0.2x &= -1 \\[5pt] {\color{blue}10} \cdot (0.2x) &= {\color{blue}10} \cdot (-1) \\[5pt] 2x &= -10 \end{align}

Then, we solve the equation using the multiplication principle, as usual:

\begin{align} 2x &= -10 \\[5pt] \dfrac{2x}{2} &= \dfrac{-10}{2} \\[5pt] \dfrac{\cancel{2}x}{\cancel{2}} &= -\dfrac{10}{2}\\[5pt] x &=-5 \end{align}

FLAG

What is the solution to the equation 0.9s=3.6?

EXPLANATION

First, we multiply both sides of the equation by 10 to get rid of the decimals:

\begin{align*} \require{cancel} 0.9s&=3.6\\[5pt] 10 \cdot (0.9s) &= 10 \cdot (3.6)\\[5pt] 9s &= 36 \end{align*}

Then, we solve the equation using the multiplication principle, as usual:

\begin{align*} \require{cancel} 9s &= 36\\[5pt] \dfrac{9s}{9} &= \dfrac{36}{9}\\[5pt] \dfrac{\cancel{9}s}{\cancel{9}} &= \dfrac{36}{9}\\[5pt] s&=4 \end{align*}

FLAG

What is the solution to the equation $0.2y = 1?$

a
$y=5$
b
$y=10$
c
$y=2$
d
$y=20$
e
$y=0.5$

Solve for $x$, if $0.3x=-3.3.$

a
$x=-11$
b
$x=-7$
c
$x=14$
d
$x=11$
e
$x=-9$

If $0.4w=-6$, then $w =$

a
$-3.75$
b
$-15$
c
$14.5$
d
$-1.5$
e
$-18$

How do we get rid of the decimal in an equation like

0.25x = 2,

when there is more than one number behind the decimal place? If we multiply by 10 as usual, we shift the decimal place over one spot to the right:

\begin{align*} 0.25x &= 2 \\[5pt] 10 \cdot (0.25x) &= 10 \cdot (2) \\[5pt] 2.5x &= 20 \end{align*}

However, there is still one number behind the decimal place. So, we can multiply by 10 again:

\begin{align*} 2.5x &= 20 \\[5pt] 10 \cdot (2.5 x) &= 10 \cdot (20) \\[5pt] 25x &= 200 \end{align*}

Now, there are no numbers behind the decimal place, so we can continue with the usual method of applying the multiplication principle:

\begin{align*} \require{cancel} 25x &= 200 \\[5pt] \dfrac{25x}{25} &= \dfrac{200}{25} \\[5pt] \dfrac{\cancel{25}x}{\cancel{25}} &= \dfrac{200}{25} \\[5pt] x &= 8 \end{align*}

Looking back, we can see a faster way to apply the same method. We multiplied by 10 twice, which means that overall, we multiplied by 100. In general, multiplying a decimal by 100 shifts the decimal place over two spots to the right. So, we could have solved the equation faster by multiplying by 100.

\begin{align*} 0.25x &= 2 \\[5pt] 100 \cdot (0.25x) &= 100 \cdot (2) \\[5pt] 25x &= 200 \\[5pt] \dfrac{25x}{25} &= \dfrac{200}{25} \\[5pt] \dfrac{\cancel{25}x}{\cancel{25}} &= \dfrac{200}{25} \\[5pt] x &= 8 \end{align*}

FLAG

What is the solution to the equation 0.25s=0.5?

EXPLANATION

First, we multiply both sides of the equation by 100 to get rid of the decimals:

\begin{align*} \require{cancel} 0.25s&=0.5\\[5pt] 100 \cdot (0.25s) &= 100 \cdot (0.5)\\[5pt] 25s &= 50 \end{align*}

Then, we solve the equation using the multiplication principle, as usual:

\begin{align*} \require{cancel} 25s &= 50\\[5pt] \dfrac{25s}{25} &= \dfrac{50}{25}\\[5pt] \dfrac{\cancel{25}s}{\cancel{25}} &= \dfrac{50}{25}\\[5pt] s&=2 \end{align*}

FLAG

Solve for $x$, if $0.15x=4.5.$

a
$x=3$
b
$x=30$
c
$x=45$
d
$x=20$
e
$x=10$

If $0.16w=-1$, then $w =$

a
$-0.16$
b
$-12.5$
c
$-16$
d
$-6.25$
e
$25$

Solve for $t$, if $-0.25t=1.$

a
$t=4$
b
$t=1.25$
c
$t=3.5$
d
$t=-8$
e
$t=-4$

If 0.25+0.03z=1, then what is the value of z?

EXPLANATION

First, we multiply both sides of the equation by 100 to get rid of the decimals:

\begin{align*} \require{cancel} 0.25+0.03z&=1\\[5pt] 100 \cdot (0.25+0.03z)&=100 \cdot (1)\\[5pt] 100 \cdot (0.25)+100 \cdot (0.03z) &= 100\\[5pt] 25 + 3z &= 100 \end{align*}

Then, we solve the equation using the addition and multiplication principles, as usual:

\begin{align*} \require{cancel} 25 + 3z &= 100 \\[5pt] 3z + 25 &= 100 \\[5pt] 3z + 25-25 &= 100-25 \\[5pt] 3z &= 75\\ \dfrac{\cancel{3}z}{\cancel{3}} &= \dfrac{75}{3}\\[5pt] z&= 25 \end{align*}

FLAG

If $1+1.5p=4$, then $p =$

a
$-4$
b
$2$
c
$3$
d
$4$
e
$5$

If $0.3+0.35x=1,$ then $x=$

a
$x=35$
b
$x=1$
c
$x=-2$
d
$x=2$
e
$x=3$
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