# Related rates

### Related rates

Related rates come in handy when we have two related quantities and one of their rates of change is much harder to find than the other one. For example, look at the figure below, you can see that it is difficult to find the rate of change in radius of the balloon while it is being pumped up. However, the rate of change in volume of the balloon can be easily found if we know the air flow rate of the pump. Therefore, the work left with us is just to find the equation that relates the two related quantities, and then use the Chain Rule to differentiate both sides with respect to time.