# Z varies jointly with x and y when x=7 and y=2, z=28. How do you write the function that models each variation and then find z when x=6 and y=4?

Jun 29, 2015

The function is $z = 2 x y$. When $x = 6$ and $y = 4$, $z = 48$.

#### Explanation:

We know that the function has the form

$z = k x y$, so

$k = \frac{z}{x y}$.

If $x = 7$, $y = 2$, and $z = 28$,

k = 28/(7 × 2)= 28/14 = 2.

So

$z = 2 x y$

If $x = 6$ and $y = 4$,

z = 2 × 6 × 4 = 48