Hastly, search google for a more throughly one:
Achilles and a tortoise raises. the tortoise starts ahead of achilles, let's call the distance d. In order for achilles to pass the turtle, he must pass the point the turtle is at now. When achilles has reached the point d, the tortoise has moved another small distance, d2. When achilles has reached d+d2, the tortoise has moved the distance d3, and so on, whenever achilles has come closer to the tortoise, it has moved another small distance and draws the conclusion, achilles will never reacht he trutle.