When I first saw this one, I thought it might be a chance to use some of the Erlang queueing equations, which I’ve known about for ages but never used seriously. Instead, I think it’s a bit easier than that. I missed the cutoff for having my name picked though!
My strategy of starting with the easy cases and building out to more complex cases was used successfully by other solvers. My analysis of the easy cases was correct, but there was a mistake in the way I built out. My diagram probably didn’t help; the one drawn by the winner didn’t distinguish between the larger and smaller piles, and I think that’s where my error crept in.
For example, when I considered (9, 5), I thought it was a losing position because I didn’t see that taking six coins from the larger pile produced (5, 3), since the larger pile became the smaller pile in that move. So the “simplification” I introduced, of specifying one pile as larger, while not wrong, made it easier for me to make a mistake. It helped to break my mental model by suggesting an identity for the piles (“larger” or “smaller”) that isn’t persistent, but depends on the progress of the game. Will try not to do that again!
This spread sheet is my own attempt to show how the collateral flow to or from a clearing house works. I created it about five years ago when I was working at a bank, and needed to explain the relationships between different quantities, and how they are calculated.
If you have a rough idea of how futures work, and want to see a detailed example, this post might help. If you don’t know what futures are, this won’t help, but Wikipedia’s intro might.
At the end of November last year, my girlfriend and I decided to try a diet box company. We chose wsmaq after trying one-day samples from them and one other company; the food from wsmaq was noticeably better.
Initially I thought this week’s Classic puzzle might be too tough to solve without some serious insights, but the more I thought about it, the more it seemed like I might be able to break it down to manageable pieces.
I’ve had this mental model for a while, but it solidified a year ago after explaining it at work, and I wanted to use it again in a Twitter debate shortly afterwards. Twitter’s the wrong place for real explanations though, so here it is.
This model will not solve your disagreements for you, and it’s not a substitute for calculating the NPV of your possible projects. Instead, it’s a quick shorthand that might make discussions more useful, and show you something about your team.