Plotting a graph takes time. Often mathematicians just want to know the key features. These are: shape, location and some key points (such as where the graph crosses the axes or turning points).

Real life situations such as travelling over time and across distance can be drawn on a graph. Exact distances and times are plotted on the graph. These are shown as co-ordinates. These points are ...

Problem: How many colors are needed so that if each point in the plane is assigned one of the colors, no two points which are exactly distance 1 apart will be assigned the same color? This problem has ...