Question 329214
When two variable quantities have a constant (unchanged) ratio,
their relationship is called a direct variation. 
It is said that one variable "varies directly" as the other.  

The constant ratio is called the constant of variation.

The formula for direct variation is y = kx,
 where k is the constant of variation.
"y varies directly as x"

In a direct variation, the two variables 
change in the same sense.  If one increases, so does the other.


Example:
     
The weekly salary Rita earns, R, varies directly as the number of hours, h, which she works.  Express this relation as a formula.

R = hk