Harry Potter and the Methods of Rationality

On the other hand, one competent hedge fundie could probably own the whole wizarding world within a week. Harry filed away this notion in case he ever ran out of money, or had a week free.

Meanwhile, the giant heaps of gold coins within the Potter vault ought to suit his near-term requirements.

Harry stumped forward, and began picking up gold coins with one hand and dumping them into the other.

When he had reached twenty, Professor McGonagall coughed. "I think that will be more than enough to pay for your school supplies, Mr. Potter."

"Hm?" Harry said, his mind elsewhere. "Hold on, I'm doing a Fermi calculation."

"A what?" said Professor McGonagall, sounding somewhat alarmed.

"It's a mathematical thing. Named after Enrico Fermi. A way of getting rough numbers quickly in your head..."

Twenty gold Galleons weighed a tenth of a kilogram, maybe? And gold was, what, ten thousand British pounds a kilogram? So a Galleon would be worth about fifty pounds... The mounds of gold coins looked to be about sixty coins high and twenty coins wide in either dimension of the base, and a mound was pyramidal, so it would be around one-third of the cube. Eight thousand Galleons per mound, roughly, and there were around five mounds of that size, so forty thousand Galleons or 2 million pounds sterling.

Not bad. Harry smiled with a certain grim satisfaction. It was too bad that he was right in the middle of discovering the amazing new world of magic, and couldn't take time out to explore the amazing new world of being rich, which a quick Fermi estimate said was roughly a billion times less interesting.

Still, that's the last time I ever mow a lawn for one lousy pound.

Harry wheeled from the giant heap of money. "Pardon me for asking, Professor McGonagall, but I understand that my parents were in their twenties when they died. Is this a usual amount of money for a young couple to have in their vault, in the wizarding world?" If it was, a cup of tea probably cost five thousand pounds. Rule one of economics: you can't eat money.

Professor McGonagall shook her head. "Your father was the last heir of an old family, Mr. Potter. It's also possible..." The witch hesitated. "Some of this money may be from bounties placed on You-Know-Who, payable to his ki- ah, to whoever might defeat him. Or those bounties might not have been collected yet. I am not sure."

"Interesting..." Harry said slowly. "So some of this really is, in a sense, mine. That is, earned by me. Sort of. Possibly. Even if I don't remember the occasion." Harry's fingers tapped against his trouser-leg. "That makes me feel less guilty about spending a very tiny fraction of it! Don't panic, Professor McGonagall!"

"Mr. Potter! You are a minor, and as such, you will only be allowed to make reasonable withdrawals from -"

"I am all about reasonable! I am totally on board with fiscal prudence and impulse control! But I did see some things on the way here which would constitute sensible, grown-up purchases..."

Harry locked gazes with Professor McGonagall, engaging in a silent staring contest.

"Like what?" Professor McGonagall said finally.

"Trunks whose insides hold more than their outsides?"

Professor McGonagall's face grew stern. "Those are very expensive, Mr. Potter!"

"Yes, but -" Harry pleaded. "I'm sure that when I'm an adult I'll want one. And I can afford one. Logically, it would make just as much sense to buy it now instead of later, and get the use of it right away. It's the same money either way, right? I mean, I would want a good one, with lots of room inside, good enough that I wouldn't have to just get a better one later..." Harry trailed off hopefully.

Professor McGonagall's gaze didn't waver. "And just what would you keep in a trunk like that, Mr. Potter -"

"Books."

"Of course," sighed Professor McGonagall.

"You should have told me much earlier that sort of magic item existed! And that I could afford one! Now my father and I are going to have to spend the next two days frantically hitting up all the secondhand bookshops for old textbooks, so I can have a decent science library with me at Hogwarts - and maybe a small science fiction collection, if I can assemble something decent out of the bargain bins. Or better yet, I'll make the deal a little sweeter for you, okay? Just let me buy -"

"Mr. Potter! You think you can bribe me?"

"What? No! Not like that! I'm saying, Hogwarts can keep some of the books I bring, if you think that any of them would make good additions to the library. I'm going to be getting them cheap, and I just want to have them around somewhere or other. It's okay to bribe people with books, right? That's a -"

"Family tradition."

"Yes, exactly."