I like the attempt to make everything interactive and fun! But in this case, the concept of probabilities summing to 1 is simple enough that I think most of the interactive examples detract from the learning instead of adding. I think having just one interactive example for this notebook, the first one with a scale, is sufficient.

Made some changes accordingly. Current notebook explains the axioms with appropriate examples. Kept the first interactive example at the start (with the scale) the same.

Hope it's good now.

Closing this PR now; new one up here: #31