He laid it out as simply as it deserved.
'I have reason to believe I know how every match plays out,' he said. 'Not the specific scores on most of them. The outcomes. Every match, every round.'
He gave them the results: Transylvania over England, Luxembourg over Scotland, Uganda over Wales. Ireland through the semi-final. Ireland winning the final.
The room received this in different ways. Hermione looked at him with the expression she had when she was deciding whether something belonged in the category of information he shouldn't have or something the eidetic memory produced that I haven't anticipated. Harry had already moved past the question of how, visibly, and was thinking about the implications. Sirius looked interested in the specific way of someone who had spent twelve years solving problems with whatever was available and found Ron's available materials impressive.
Percy looked the way Percy always looked when someone stated something precise without fully explaining the mechanism: professionally sceptical, pending evidence.
'How?' Percy said.
'The same way I know things I shouldn't know,' Ron said. 'You've all seen it for two years. The side effect of the charm in second year was cognitive enhancement. I see patterns others miss.' He paused. 'Some of what I analyse turns out to be useful. And I had plenty of time for analysis during my trip.'
Percy absorbed this with the expression of someone applying his analytical framework to a claim that was outside the framework's normal operating range, finding it provisionally acceptable, and filing it accordingly. Which was, as it happened, the Percy version of trust.
'The Goblins run a proper betting market,' Ron continued. 'Not the high-street shops — those are fine for small positions, but they build their margin into the odds and cap the maximum stake. Gringotts operates a real market. They set the price based on genuine expectation, charge a small transaction percentage, and the counterparty exposure is unlimited in principle. If you know the outcome, the returns are very clean.'
'What are the returns?' Bill said. He was leaning forward slightly. The Gringotts curse-breaker's attention, precise and financially fluent. 'Walk us through it.'
Ron walked them through it.
Total pool entering the first bet: one hundred and fifty-one thousand, nine hundred Galleons, across all accounts combined. Compounded through five sequential bets, each result reinvested entirely before the next match.
Transylvania over England: the Goblins would price England with market respect they hadn't earned. One point five multiplier. After bet one: two hundred and twenty-seven thousand, approximately.
Luxembourg over Scotland: one point eight multiplier. After bet two: four hundred and ten thousand.
Uganda over Wales: this was the one that mattered most for the mathematics. Two to one odds, because the European-biased market would underestimate an African champion side, and the Goblins' market, while sharper than most, still drew on a pool of opinion that skewed heavily toward the familiar. After bet three: eight hundred and twenty thousand.
Ireland over Peru in the semi-final: one point five. After bet four: one point two million.
Ireland over Bulgaria in the final: one point eight, because Krum made this genuinely close and the market would reflect it. After bet five: two million, two hundred and fourteen thousand Galleons.
He let the number sit.
'From one hundred and fifty-one thousand, nine hundred,' he said. 'Conservatively, ten to fifteen times your stake.'
The room was quiet in the way of people doing arithmetic and arriving at the same answer.
He did not add the rest of the calculation. The figure he had given them was honest as a floor. The five certain bets compounded to fourteen point six times — within the range he had quoted. But the Gringotts accounts could also be positioned on the group stage matches he had inferred from the full bracket: eighteen of the twenty-one tournament fixtures, running in parallel alongside the five certain bets, their winnings settling separately and adding to the total. The group stage ran first. By the time the five certain bets began, the pool would already be larger than what he had shown them — the parallel group stage winnings folding into the base before the knockout compound started. The floor he had quoted assumed the starting capital unchanged. The ceiling assumed the group stage had done its work first. The actual figure, if the group stage performed as he expected, was closer to thirty-five times. He had given them the floor because the floor was sufficient to secure their commitment, and because overpromising was a habit he found structurally unsound. 'Each person's return,' he said, 'is proportional to what they put in. This is not a shared pot with shared returns. Every account is separate. The coordination is mine. The money is yours.'