here's a conversation from my past:
buddy: please explain to <manager> why you can't average daily totals for a weekly average.
me: ---remembers manger plays softball and accompanying titillating rumors---
me: okay, let's say week one you go 0 for 1 and week two you go 4 for 4. what's your batting average?
me: no it isn't, it's .500
buddy: yes! i knew you could do it, i've been trying to explain it for half an hour!
me: ---goes back to sweeping pepperonis and mushrooms under oven---
with that said