If y varies inversely with x, and y = 5 when x = 7, what is the value of y when x = 4?

Question

10828 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2016-07-07T13:35:48

$y = 8 \frac{3}{4}$ $y = 8 3/4$ when $x = 4$ $x = 4$

An inverse variation: $y = \frac{k}{x}$ $y = k/x$

We are given $y$ $y$ and $x$ $x$ . We need to solve for $k$ $k$ so we can find $y$ $y$ when $x$ $x$ equals $4$ $4$ .

$5 = \frac{k}{7}$ $5 = k/7$

$7/1 * 5 = k/cancel7 * cancel7/1$

$35 = k$

We found what $k$ is, so know we can make our inverse variation equation.

$y = 35/x$

Now let's plug in $4$ for $x$ to find $y$ .

$y = 35/4$

$y = 8 3/4$