“Only sufficiently frequent attacks, with increasing force, will result in eradication, assuming the available resources can be mustered in time,” they concluded...
How fast do we need to deal with the outbreak? Here’s the equation they used, where S = susceptibles, Z = zombies and R = removed. If an infection breaks out in a city of 500,000 people, the zombies will outnumber the susceptibles in about three days.
check out the math:
I imagine that the big letter "Z" in the middle is a symbol for # of Zombies.