Explore 2-dimensional world:

Take a tour inside the Klein bottle:

One day a little kitten was sitting on the ladder.

Exactly in the middle.

The vertical position is very unstable. So ladder fell on the ground. It was dropping so that its upper end was sliding on a vertical wall, and the lower end  was sliding on the ground.

Trace the trajectory of the kitten (red spot) - the middle of the ladder.

Trace the trajectory of the kitten in case when kitten is not in the middle of the ladder.

Trace the trajectory of red spot on the small circle (twice less than big)

Trace the trajectory of red spot on the small circle (1/4 case)

Trace the trajectory of red spot on the small circle (common case)

Explore Conic sections

Explore Cube sections

Introduction to Permutations and Combinations

How to Calculate Permutations and Combinations from 5 Objects

3 at a time

How to Calculate the Odds of Winning the Lottery

How to calculate losing at the lottery