CARD · 04.A
BAYES
When yesterday updates today. Bayes is the patient friend who says: "tell me what you knew, and I'll tell you what you know now."
P(A|B) = P(B|A) · P(A) / P(B)
PROBABILITY STREET PRESS — VOL · 02
확률 PROBABILITY 確率
from corner-store coin-flips to cosmic certainty
FIELD NOTE 001
"a coin doesn't remember the last toss — and that, friend, is the whole secret."
EDITOR'S STAMP
P(today)
≈ 0.500
± a smile
SEC · 02
EDITOR'S NOTE
Probability is the friendliest math we have. It's the math of "maybe."
Welcome to the second volume of the Probability Street Press. We took the chalkboard outside, taped it to a streetlamp, and asked: what does the math of chance look like when you let it loose into the city?
What you'll find here are eight pages of friendly arithmetic, hand-stamped diagrams, and one or two tools you can roll yourself. There's a calculator. There's a die. There's a pull-quote you'll probably tape to your fridge.
Every illustration on this page draws itself for you, the way a friend would sketch on a napkin while explaining. None of it is automated; all of it is invitation.
SEC · 03
THE ROLL
A small interactive bench. Choose a number of sides on your hypothetical die, and we'll roll it together.
OUTCOME
—
Probability of this face: 1 / 6 ≈ 16.67%
RECENT ROLLS
- — roll the die to begin a streak —
SEC · 04
THREE FRIENDS
Three concepts that live next door to each other on Probability Street.
CARD · 04.B
BERNOULLI
A coin, again and again. Bernoulli counts the heads in a hundred flips and shrugs gently when the answer is just "about half."
P(k) = C(n,k) · pᵏ · (1−p)ⁿ⁻ᵏ
CARD · 04.C
BELL CURVE
The friendly hill. Add enough small randomnesses together and they all huddle politely around the middle. It happens almost everywhere.
f(x) = (1/σ√2π) · e^(−(x−μ)² / 2σ²)
SEC · 05
FIELD GUIDE
Six pieces of street probability you will recognize once you start looking.
FG · 01
ROULETTE WHEEL
38 pockets, one ball, infinite stories. The casino's gentle reminder that 1/38 is enough of an edge for empires.
FG · 02
GALTON BOARD
Drop a thousand marbles, watch them argue with gravity, and a bell curve assembles itself at the bottom.
FG · 03
COIN STACK
A stack of independent flips. Each one fresh; none of them remembering the last. The math of forgiveness.
FG · 04
SHUFFLED DECK
52 cards, 8.07 × 10⁶⁷ permutations. Most decks ever shuffled were unique to history. Yours included.
FG · 05
URN MODEL
Reach in. Pull out a marble. Put it back, or don't. The whole field of sampling fits inside one earthenware jar.
FG · 06
PIE OF EVENTS
A whole that adds to one. The friendliest constraint in mathematics: somebody, somewhere, must win.
If you walked through this issue from front to back, thank you. If you skipped to this last spread first, hello — that was probably the right move.
Probability isn't a way to predict tomorrow. It's a way to be a little kinder to yourself about what didn't go as planned. The dice were always going to land somewhere; the world was always going to choose one branch of the tree.
Roll often. Update gently. Keep good company. — the editor
Until vol. 03, hwaglyul · 確率 · probability