Joint Variation
Jointly Proportional
When we say z is jointly proportional to a set of variables, it
means that z is directly
proportional to each variable taken one
at a time.
If z varies jointly with respect to x and y,
the equation will be of the form z = kxy (where k is
a constant).
Equation:
c =
5ab
Variable c is jointly proportional
to a and b. That means c is
directly proportional to both a and b.
Doubling a causes c to double. Doubling b causes c to
double. Doubling both a and b causes c to
quadruple.

a 
b 
c 
1 
1 
5 
2 
1 
10 
1 
2 
10 
2 
2 
20 

See
also
Inverse variation, gravity
