Beginning Algebra With Applications, Chapter 4, 4.1, Section 4.1, Problem 40

Greenland, the largest island in the world is 21 times larger than Iceland. The combined area of Greenland and Iceland is $880,000$ mi$^2$. Find the area of Greenland.

If we let $x$ and $y$ be the area of Greenland and Iceland respectively, we have

$x+y = 880,000 \qquad$ Equation 1

And

$x=21y \qquad$ Equation 2

By substituting equation 2 to equation 1,


$
\begin{equation}
\begin{aligned}

(21y) + y =& 880,000
\\
22y =& 880,000
\\
y =& 40,000

\end{aligned}
\end{equation}
$


Then, by using back substitution, we get


$
\begin{equation}
\begin{aligned}

x =& 21y
\\
x =& 21 (40,000)
\\
x =& 840,000

\end{aligned}
\end{equation}
$


Thus, the area of Greenland is $840,000$ mi$^2$.