The Underwear Ratio

Being a bachelor - NOT a 'confirmed bachelor,' thank you very much - I have developed my own way of doing household chores. Since I used to be a cook, I really do wash dishes promptly, I keep my kitchen pretty clean and my knives sharp, and I take the trash out regularly. I also keep the carpets swept and the furniture polished and vacuumed.
   When it comes to laundry, though, I have developed my own formula. I realized early on that the frequency with which I would have to do laundry correlated directly with the amount of underwear I owned. The more underwear that I owned, the less frequently I would have to do laundry. I had enough shirts and pants to wear to work, shorts and t-shirts to wear otherwise, and plenty of socks to go around. I didn't need to wash the shirts every time I wore them, unless I wore them for a long period of time, but I wasn't going to compromise on underwear; one and done, as it were. When I ran out of clean underwear - getting close to the emergency stash - I would be forced to wash clothes.
   The formula is this: the need to do laundry, N, is like a probablility, it ranges from 0 - absolutely no need - to 1 - an urgent certainty. That probability curve is represented by the number of dirty underwear, D, divided by the total number of underwear available including emergency pair, T, times the days since I last did laundry, E, divided by the number of days of non-emergency underwear, R (not T again). That would be:
   N = (D/T) * (E/R)
   You can see that as the ratios increase N approaches 1, meaning I must do laundry. To make it less abstract, let's substitute values. I have 24 pair of regular underwear and 3 pair of emergency underwear. If it's been 7 days since I last did laundry, the ratio would be:
   N = (7/27) * (7/24)
or
   N = 0.259 * 0.291
or
   N = 0.08
No real urgency to do laundry.

   If, however, we gor forward two weeks, the numbers become
   N = (21/27) * (21/24)
or
   N = 0.680
This is EIGHT TIMES the underwear urgency than two weeks before. That's pretty serious.

   You might say that D and E should always be equal, but you'd be wrong. There's nothing that says I have to actually wear underwear every day.

    Economics note: Underwear is a depreciating asset. And the more you wear it the faster it wears out. Some guys I know will wear a waistband with scraps of fabric attached and call it underwear, but not me, I adhere to strict depreciation schedule. And when I throw out a set, I tear it in half, so no one else would be tempted to put them on.