Hands-on math, taught calmly. Twenty bite-size lessons, seven interactive simulators, twelve formulas with worked examples — every result computed locally on your device. No streaks. No XP. No internet required.
From "what is probability" to the Central Limit Theorem. Each lesson ends in a 3-question knowledge check with instant explanations. No time pressure, no failure shame.
Outcomes, sample spaces, and the basic vocabulary of chance.
The long-run average of a random outcome — what 3.5 means for a six-sided die.
How to update what you believe when new evidence arrives.
Why sample means turn into a bell curve, no matter where they start.
Monty Hall, Two-Children, Birthday — the classics, explained step by step.
Weather forecasts, medical tests, and traffic — probability is everywhere.
Run a thousand coin flips and watch the running mean settle on 0.5. Configure a probability wheel, tug its weights, and see the segment probabilities recompute instantly. Every chart snaps to its final state — no spin animations, no celebration confetti, just the math.
Define segments by label and weight. The wheel doesn't spin — it computes the chosen outcome and shows you exactly what fraction of the total weight that segment carries.
Drag a slider for room size; the curve recalculates. The "paradox" name oversells it — once you see the multiplication, it's just counting pairs.
Drop a thousand random points inside a unit square. Count how many fall inside the inscribed quarter-circle. Multiply that ratio by four. That number is π — or near enough, depending on how many points you threw.
Each formula carries a worked example and an inline calculator that recomputes instantly as you adjust its sliders. No LaTeX, no jargon walls.
Build your own random experiment. Define outcome labels and weights, pick a sample size, run it, see the histogram and the summary stats. Save configurations locally; come back to them later.
One short rotating fact, refreshed each day, picked deterministically by the calendar so everyone sees the same fact on the same day. Tap to jump straight to the related lesson. Optional once-per-day local notification reminder — off by default.
Home — your daily insight, today's simulator, and where you left off
All twenty lessons, with a quiet progress meter at the top
A lesson — read, then take a 3-question knowledge check
Probability wheel — define segments, see the math
Birthday paradox — slide for room size, watch the curve
Monte Carlo π — random points, classic estimate
Formula reference with an inline calculator
Get Roll & Tell for Android. Lessons, simulators, reference, and sandbox — all bundled, all offline.
Requires Android 8.0 or later. iOS in the works.
