Zombies meet Mathematics

Below is how I brought in "28 days later", "World War Z", or "The walking dead" into my calculus class to introduce points of inflection.  At this point my students have been taught derivative rules, relative maximums and minimums, but not yet application of second derivatives.

First ask the class

What would the graph of "Zombie population" vs "time" look like?

Have them explain their answers and why.  Instead of telling them, play the following game.
1) Number the students from 1- X
2) Put a table on the board with Days, and Number of Zombies as the headings.
3) Draw a random number (I used a simple random number generator)-The number becomes the Zombie.
4) Each following day draw N numbers where N= the number of zombies on the previous days.  If the number of a student is drawn they become a zombie and will attack the next day.

Your chart should probably start like:

On Day 2 you would have drawn 1 number, on day 3 you would have drawn 2 numbers, etc.

Of course, it will slowly stop doubling due to some numbers being drawn more than once.  For example if number "10" was drawn on day 2, and again on day 3, then it represents a case where a zombie attacked another zombie (stupid zombies!).

You can then graph the data and it should look like a horizontally stretched out "S". 

Now lets integrate calculus. I used the following equation, (however if you find, or create, a better equation please let me know) Also you could also use base 2, as it looks very similar.  My world ends roughly after 28 days (since I love the show 28 days later).

Where Z(t) is the population of zombies, in billions, at year t.  The graph should be

From here you can answer the following questions:

Now you want them to lead you towards points of inflections, so here is how I suggest you do it:

At this point we have discussed relative maximums and minimums are there any of these on the graph? No.  Alright, is there anything "special" going on?

Then let them talk, explain, discuss.  You want them pointing towards the middle, and determining that the derivative here is a maximum.  You can then relate how you determine relative maximums of functions to determine that you simply make the second derivative equal 0.  This is what we call a Point of Inflection!

Please change, tweak, use, etc as you see fit.