3. If the man walks 3000...

3. If the man walks 3000 kilometers per hour. The swimming pool is 1 kilometer away. We know that the time is

proportional to the distance and the time is inversely proportional to the speed.

what on earth is the whole picture of calculus?

Calculus is the key for scientists,engineers and economists to grasp the world. In the previous example, we worked out the time for arriving at some place at a given speed. Speed is the rate of change in displacement.

Change is the nature's content. Economy, stars,transportation and population are changing with time. We need an appropriate mathematical tool to grasp them. It is calculus. Isaac Newton was one of the investors of calculus. The invention was for the purpose of using it as a tool to accurately calculate the displacement, sweet of planets and comets and their trajectories under the gravitational influence.