The U.S. Postal Service handles 170,000,000,000 pieces of mail each year. This is 40% of the world’s total. How many pieces of mail are sent each year?

May 27, 2017

See a solution process below:

Explanation:

We can rewrite this as:
$170$ billion is 40% of what?

"Percent" or "%" means "out of 100" or "per 100", Therefore 40% can be written as $\frac{40}{100}$.

When dealing with percents the word "of" means "times" or "to multiply".

Finally, lets call the number of pieces of mail we are looking for "m".

Putting this altogether we can write this equation and solve for $m$ while keeping the equation balanced:

$170 = \frac{40}{100} \times m$

$\frac{\textcolor{red}{100}}{\textcolor{b l u e}{40}} \times 170 = \frac{\textcolor{red}{100}}{\textcolor{b l u e}{40}} \times \frac{40}{100} \times m$

$\frac{17000}{\textcolor{b l u e}{40}} = \frac{\cancel{\textcolor{red}{100}}}{\cancel{\textcolor{b l u e}{40}}} \times \frac{\textcolor{b l u e}{\cancel{\textcolor{b l a c k}{40}}}}{\textcolor{red}{\cancel{\textcolor{b l a c k}{100}}}} \times m$

$425 = m$

$m = 425$

425 billion or 425,000,000,000 pieces of mail are sent each year.