Two of my favorite things ;P
The zombie apoc has started! But thanks to the new Zombie Preparedness Plan put forth by the Pentagon, humans have a 50% chance of leaving an encounter with a zombie unscathed. Assume we are at the beginning of the outbreak, and assume the number of encounters b/w zombies and humans is proportional to the product of their proportions.
Some studies done have shown that an average person encounters ~13 other people a day. Assuming this holds, how long until half the population is munching on brains?