Answer
$x = 5$
Work Step by Step
Our equation for an inverse variation is $y = \frac{k}{x}$ or $xy = k$ or, as will be needed in this problem, $x = \frac{k}{y}$. We will use the second form of the equation to solve for k.
We use the ordered pair (2.5,4) to solve for k, from which we know that $x = 2.5$ and $y = 4$.
$2.5\times4 = k$
$ 10 = k$
So, $k = 10$
Therefore, our equation for the inverse variation is $y = \frac{10}{x}$ or $xy = 10$ or $x = \frac{10}{y}$
Using the third form of the equation, $x = \frac{10}{y}$, we can use the y value of the second order pair to find our missing x value.
$x = \frac{10}{2}$
$x = 5$
