Rate of Change is used to describe the ratio of a change in one variable compare to a change of another variable

If there is a function $f(x)=y$ then the rate of change of the function $f(x)$ correspond to the rate of change of variable z is

- ${\frac {\Delta y}{\Delta x}}={\frac {\Delta f(x)}{\Delta x}}$

If there are two points $(1,3)$ and $(2,7)$

- ${\frac {\Delta y}{\Delta x}}={\frac {\Delta f(x)}{\Delta x}}={\frac {7-3}{2-1}}=4$