# Calculus 1 : How to find rate of change

## Example Questions

### Example Question #21 : How To Find Rate Of Change

Find the rate of change of a function  from  to .

Explanation:

We can solve by utilizing the formula for the average rate of change: .

Solving for f(x) at our given points:

Plugging our values into the average rate of change formula, we get:

.

### Example Question #22 : How To Find Rate Of Change

Find the rate of change of a function  from  to .

Explanation:

We can solve by utilizing the formula for the average rate of change: .

Solving for f(x) at our given points:

Plugging our values into the average rate of change formula, we get:

.

### Example Question #23 : How To Find Rate Of Change

A spherical balloon is inflating at rate of 0.1 cubic meters per second. Find the rate of change of the surface area of the balloon (in square meters per second) when the balloon has a radius of 1 meter.

Explanation:

The volume of a sphere is given by

, where r is the radius of the sphere.

The surface area of a sphere is given by  (r is the radius of the sphere). The rate of change of the volume of the sphere is found by taking the first derivative of the function for volume:

, where  is the change of the radius with respect to time.

This derivative was found by using the power rule

The rate of change of the surface area of the sphere is found the same way, instead using the function for surface area:

.

The balloon's volume is increasing at a constant rate of 0.1 cubic meters per second when the radius of the balloon is 1 meter, thus plugging in these values into the  equation gives us the following:

. Solving for , we get  meters per second. Since we are solving for the rate of change of surface area of the balloon, we plug this value into its equation along with the radius we want (1 m). Solving for the rate of change of the surface area we get:

square meters per second.

### Example Question #21 : How To Find Rate Of Change

The spherical bottom of a snowman is melting such that its volume is decreasing at a rate of

What is the rate of change of the radius, to the nearest whole number, when the radius is ?

Explanation:

First, find the rate of increase in the radius :

Next, take the derivative of the area of a circle () by using the Power Rule ():

Lastly, plug in the givens and simplify:

### Example Question #22 : How To Find Rate Of Change

For which of the following functions is the average rate of change along the interval  equal to the instentaneous rate of change at ?

Explanation:

The average rate of change of a function f(x) on an interval [a,b] is given by

while the instantaneous rate of change at a is given by

.

Finding each of these on the interval [-2, 2] for the equations given:

We can see that the two rates are equal for f(x) and g(x), but not h(x).

### Example Question #26 : How To Find Rate Of Change

Find   for the equation

Explanation:

To evaluate, first take the derivatives of both sides of the equation. This gives

By factoring and simple algebraic simplification, the equation becomes

### Example Question #27 : How To Find Rate Of Change

A spherical balloon with radius  is being inflated with air. Its radius is expanding at a rate of. What is the change in volume of the sphere (in  )?

Explanation:

The volume of a sphere is given by

To find the change in volume, differentiate the volume with respect to time.

Simply plug in the values given in the problem to find the rate of change of the volume.

### Example Question #23 : How To Find Rate Of Change

For the relation , compute  using implicit differentiation.

Explanation:

To calculate  using implicit differentiation, we differentiate everything in the relation  and solve for :

So we have .

### Example Question #21 : Rate Of Change

If  models the number of books a library has a function of time (in days), at what rate was the library gaining or losing books when ?

The library was gaining 195.76 books per day.

The library was losing 19.576 books per day.

The library was gaining 19.576 books per day.

The library was losing 195.76 books per day.

The library was gaining 195.76 books per day.

Explanation:

If b(t) models the rate at which a library buys and sells books, at what rate was the library gaining or losing books when ?

We need to find an instantaneous rate of change. Rates of change can be found with derivatives. Start by finding b'(t), and then using our given t value to find our final answer:

So the library was gaining 195.76 books per day.

### Example Question #30 : How To Find Rate Of Change

Abel wants to fill a spherical ball with air to bring with him to the park. It has an initial volume of , and when Abel attaches the pumps, he sets it to inflate at a rate of . How quickly does the point where the nozzle connects move from the center of the basketball?

Explanation: