PICK ONE

An n-way bet with exact RTP. Options own zones of width pᵢ on the draw; backing option j pays RTP ÷ pⱼ on a hit, so every option returns exactly the RTP. Two equal options pay 1.9× at RTP 0.95; three pay 2.85×; five pay 4.75×. Weighted options work the same way.

2 / 3 / 5 / n optionsodds = RTP ÷ pcoin flip 1.9×
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The math

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Live API (browser module)

The engine is published as an ES module that implements the RGS provider contract and rolls locally with crypto.getRandomValues: open, valid-bets, bet, collect, with the observed balance semantics (bet debits the stake, collect credits the win, integer minor units). No server, every round live, and any round replays from its seed. Bet types: OPTION_1, OPTION_2.

import { createGame } from 'https://danvid1009.github.io/gnarone-game-math/pick-one/api/rgs.js';

const g = createGame({ preset: 'coin' });                    // presets: coin, three, five, weighted
                                                       // bet types: OPTION_1, OPTION_2
const s = g.open();                                    // session, balance 100000, chipLevels [100,200,500,1000,2500,5000,10000]
const r = g.bet({ sessionId: s.sessionId, betAmount: 1000, betType: 'OPTION_2' });   // fresh crypto seed; win in r.totalWinAmount
g.collect({ roundId: r.roundId });                                           // credits the win → { balance }

// Replay any fixture: same seed, same code path, same answer as rounds/007.json
g.bet({ sessionId: s.sessionId, betAmount: 1000, betType: 'OPTION_2', seed: 'fixture-007' });

Presets and static fixtures

Presets: coin, three, five, weighted (default coin). Each preset is a frozen configuration and its own folder: the config, derived tables and settlement rule in field.json, plus one hundred pre-drawn rounds from seeds fixture-000 … fixture-099 settled for every bet type. The same seed drives every preset, so round 007 uses the same u everywhere, and the live module reproduces any of them when given the seed.

# presets, their parameters, bet types and realised RTP over the 100 rounds
curl -s https://danvid1009.github.io/gnarone-game-math/pick-one/api/index.json

# one preset: parameters, tables (bands / odds / ladder / decks), RN intervals, how to settle
curl -s https://danvid1009.github.io/gnarone-game-math/pick-one/api/coin/field.json

# one round (000–099): seed, full outcome, settlement for every bet type
curl -s https://danvid1009.github.io/gnarone-game-math/pick-one/api/coin/rounds/007.json

# all 100 rounds of a preset (stake and win per bet type)
curl -s https://danvid1009.github.io/gnarone-game-math/pick-one/api/coin/rounds.json

# round 007 played through the real calls: request bodies and every response
curl -s https://danvid1009.github.io/gnarone-game-math/pick-one/api/coin/sample-request.json
curl -s https://danvid1009.github.io/gnarone-game-math/pick-one/api/coin/sample-response.json

Settlement rule is spelled out in each preset's field.json under how_to_settle.

Figures

Odds and simulated return for 2, 3, 5 and 8 equal options.
Odds and simulated return for 2, 3, 5 and 8 equal options.

Build it yourself

git clone https://github.com/Danvid1009/gnarone-game-math.git
cd gnarone-game-math/pick-engine
npm test
node bin/build-pick.js --n 5 --js