Answer:
Joint variation.
Step-by-step explanation:
There are four types of variation,
Direct variation : When a variable varies directly as another variable,
Example : y varies directly with x ⇒ y = kx,
Where, k is the constant of variation,
Inverse variation : When a variable varies inversely as another variable,
Example : y varies inversely with x ⇒ [tex]y=k\frac{1}{x}[/tex]
Joint variation : When a variable varies directly with two or more than two variables,
Example : y varies directly with both x and z ⇒ y = kxz
Combined variation : When a variable varies both directly and indirectly as another variables,
Example : y varies directly with x and inversely with z ⇒ [tex]y=k\frac{x}{z}[/tex]
Now, here the given expression,
y = 4mt,
Where, y, m and t are variables and 4 is the constant of variation,
⇒ y varies directly as both m and t,
⇒ y = 4mt is an example of joint variation.
