### Home > PC3 > Chapter 10 > Lesson 10.1.4 > Problem10-81

10-81.

The volume of water in a pond can be modeled by the function $V(t) = 2.5\sin(0.5t) + 4$ where $t$ is in months since January 1st, and $V(t)$ is in acre-feet. About how fast is the volume changing when $t = 2$ months? (Approximate the instantaneous rate of change at $2$ months.)

$\frac{V(2.1)-V(1.9)}{2.1-1.9}$