Abstract :
Take a US penny and give it a spin by flicking it with your finger on a tabletop. What are the chances of it coming to rest heads-up once it stops spinning? With an undamaged coin, a spirited flick and a clean level tabletop, 50-50? Or how about if you flip the same coin into the air and let it bounce on the ground and come to a stop? What are the chances of it landing heads-up now, again 50-50? And given the choice of what´s behind door number one, should you stick with your first choice or switch to what´s behind door number two or door number three? The answers may surprise you.
