For the bonus points: Well it's differentiation and there's a factorial N in there, but beyond that, I can't remember anything about this - I don't think I could differentiate anything these days and certainly not with a slide rule (or was it tables?).
Not bad! I'll give you 4/10!
For those who are interested (which will probably be no-one, including myself!) it's the derivation for the Boltzmann distribution used in statistical thermodynamics. I don't understand it.
Above : SieSmith. Lovely colours, but I'm not at all sure what it is apart from an "abstract".
Below : beauxreflets. Similar idea to mine, but I couldn't for the life of me think of anything else to photograph at the last minute. I like the reflection, but I find the whiteness at the top and the blue thingy in the background top right a little distracting.