Math Help for Section 3.4, Page 134

Checking a Solution
After
solving a proportion, you should calculate the quotient of each side of
the proportion and confirm that they are the same. For instance,
you can check that $x=2$ is the correct answer of the problem in the Concept
Summary as follows. The quotient on the left side of the equation is

    $6\div18=0.\overline{3}$

and the quotient of the right side is

    $2\div6=0.\overline{3}$.

So, the answer $x=2$ is correct. 

Study
Tip
Remember that to write a ratio of one quantity to another, both
quantities must have the same units. To convert the units of a
quantity, multiply it by the ratio of two equivalent quantities. For
instance, 1 gallon is approximately equal to 3.785 liters, so you can
write 5 gallons in liters as follows.

    $\displaystyle 5{\text{ gallons}}
\approx 5\cancel{{\text{ gallons}}} \bullet {{3.785{\text{ liters}}}
\over
{1\cancel{\text{ gallon}}}} = 5\left( {3.785}\right){\text{
liters}}=18.925{\text{ liters}}$

There is a list of unit conversions inside the back cover of the textbook.