Find y Using the Constant of Variation If z varies jointly with x and y ; when x=3 , y=8 , z=6 Find z ; when x=6 and y=4

When two variable quantities have a constant ratio, their relationship is called a direct variation. It is said that one variable varies directly as the other. The formula for direct variation is ${\displaystyle y=kx}$, where ${\displaystyle k}$ is the constant of variation.

Solve the equation for ${\displaystyle k}$, the constant of variation.

Replace the variables ${\displaystyle x}$ and ${\displaystyle y}$ with the actual values.

Use the formula ${\displaystyle x=ky}$ to substitute ${\displaystyle \frac{8}{3}}$ for ${\displaystyle k}$ and ${\displaystyle 4}$ for ${\displaystyle y}$.