|Spoiler Inside: Solution to Puzzle||SelectShow>|
After one hour, each of the eight-hour zombies has done one-eighth of the damage necessary to break though. The other has done one-sixth. This totals 13/24. The remaining 11/24 will have be done with only three zombies. Is there enough time for them to do so? They have one hour until the police show up.
If x is the number of hours it will take, the equation is x/6 + x/8 + x/8 = 11/24.
The solution is 1.1.
The police show up six minutes before the zombies break through. Sean is safe, and so is Christopher. For now, anyway.