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The DeduceQuest case-room — friendly cartoon kid-detectives cracking a hidden colour code on a deduction board and crossing off a logic grid

DeduceQuest

A wrong guess isn’t a miss — it’s a clue. Narrow a hidden code with Whittle, cross-reference with Tablo, read the grid with Nona, and test a hypothesis with Rulewright. Deducia frames every puzzle as predict → observe → explain.

Crack a case Learn to deduce

Start here

Whittle’s Code Breaker Crack a hidden colour code from feedback pegs, like Bulls and Cows. Tablo’s Logic Grid Cross off possibilities clue-by-clue until one ✓ is left per row and column. Nona’s Nonogram Fill cells purely from the row and column number clues to reveal a picture. Rulewright’s Guess the Rule Predict the hidden rule before the reveal, then reconcile — predict, observe, explain.
Brain Break Take a quiet moment between cases — a fun logic riddle or a short breather. Brain breaks help you remember what you learn.

All activities

Codes

Whittle’s Code Breaker Crack a hidden colour code from exact / colour feedback pegs, like Bulls and Cows. Rulewright’s Guess the Rule Predict the hidden rule, watch what follows and what breaks, then reconcile. The 2-4-6 game 2, 4, 6 fits a hidden rule. Test your own three numbers and find it — say first whether you expect each test to fit.

Grids

Tablo’s Logic Grid Cross off possibilities clue-by-clue until one ✓ is left per row and column. Nona’s Nonogram Fill grid cells purely from the row and column number clues to reveal a hidden picture. Name the Forcing Clue You solved WHICH — now name WHY. Pick the one clue that forces the next step.

Cases

The Interrogation Room Knights tell the truth, knaves always lie. From what each islander says, deduce every kind — one world fits. Trick Questions Brain-teasers with a twist — spot why the obvious answer is a trap.

Make one

Teach the Cast Teach a deduction move to a cast member still learning it — teaching makes it stick. Code Breaker — Pass & Play One player secretly sets a colour code, the other cracks it, then swap. Fewest guesses wins.

More

Learn to Deduce Start here — how a wrong guess becomes a clue, and how deduction actually works. Mixed Practice A short round across the kits you have played — spaced so it sticks. Quick round Quick recall of kits you have mastered. Self-paced; turn on a timer only if you want one. Deduction Rush A calm speed round — race your own best on what you already know. No penalty for a miss. Deduce Duel 2–4 players take turns on one device — same questions, highest first-try score wins. Deduce Quest — the map A progression trail through every kit — clear each stop of real practice, then move on. Progress Your levels, days active, and how each track is coming along — saved on this device.
Concept Kits — 16 kits of deduction practice

Each kit is a short round of questions with hints when you need them. From reading feedback to logic grids to the scientific method — progress stays on this device.

Kit 1: Reading Feedback Code-Breaking · 4-5 · 25 questions Kit 2: Narrowing the Field Code-Breaking · 4-5 · 25 questions Kit 3: Bulls & Cows Code-Breaking · 4-5 · 25 questions Kit 4: Grid Basics Logic Grids · 4-5 · 25 questions Kit 5: Cross-Referencing Clues Logic Grids · 5-6 · 25 questions Kit 6: Nonogram Runs Nonograms · 5-6 · 25 questions Kit 7: Contradiction & Proof Reasoning · 5-6 · 25 questions Kit 8: Forming a Hypothesis Guess the Rule · 5-6 · 25 questions Kit 9: Testing a Hypothesis Guess the Rule · 6-7 · 25 questions Kit 10: Controlling Variables Reasoning · 6-7 · 25 questions Kit 11: Nonogram Intersections Nonograms · 6-7 · 25 questions Kit 12: Information & Best Guess Scientific Method · 6-7 · 25 questions Kit 13: Probabilistic Reasoning Reasoning · 7-8 · 25 questions Kit 14: Deductive vs Inductive Reasoning · 7-8 · 25 questions Kit 15: Constructing Explanations Reasoning · 7-8 · 25 questions Kit 16: Capstone — the Scientific Method Scientific Method · 7-8 · 25 questions

More ways to play

Quiz Arena Deduction Run Trust the Logic Bot? Daily Puzzle

Same idea, another world

Something you practice here shows up somewhere else too — that's real learning that travels.

Cracking a hidden code by ruling out what the clues forbid is the same elimination that names the one suspect the evidence proves. The shared idea: deduction by elimination — cracking a hidden code by ruling out what the feedback forbids is the same elimination that names the culprit from the evidence Try SleuthLab →
DeduceQuest mascot

Meet the cast — the characters who teach this

Each one stands for an idea you’ll practice. Tap a character to read their illustrated story and hear their audio drama.

Ensemble stories — the cast together

Explore all the stories →

What next? Pick a door

Chosen from what this app is about. What you open is remembered on this device only.

Where this game comes from

Bulls and Cows, and the peg game

Bulls and Cows is a pencil-and-paper guessing game with hidden digits. In 1970 Mordecai Meirowitz, an Israeli postmaster and telecommunications expert, made a board game much like it, with coloured pegs. A plastics company near Leicester, England, Invicta, sold the peg game from 1971.

One thing to hold: A plastic board with rows of holes, a hidden row of four coloured pegs behind a shield, and small black and white pegs for the answers.

Why it matters: Every answer rules codes out. In the 1970s the computer scientist Donald Knuth showed that a careful player can always find any of the 1,296 codes in five guesses or fewer.

What we don’t know: Nobody knows who first played Bulls and Cows or when. It may be about a century old.

Dates:

  1. 1970 Mordecai Meirowitz makes the peg version.
  2. 1971 Invicta Plastics starts selling the peg game.
  3. 2021 A daily five-letter word game puts the same loop online, with letters instead of pegs.

Sources: Donald E. Knuth, “The Computer as Master Mind”, Journal of Recreational Mathematics 9 (1976–77) · Wikipedia, “Mastermind (board game)” · Wikipedia, “Bulls and Cows” · Wikipedia, “Wordle” (the 2021 word game)

📚 Books for DeduceQuest

Read the story, print a workbook, or color the cast — free PDFs to read offline or print at home.

Browse all books →

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