Numbers & chance
Math mysteries
Play with numbers and shapes until the surprise shows. 20 works
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Angle Puzzles
Find the angle marked “?”.
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Tower of Hanoi
Move a smaller tower to unlock a bigger one.
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Water Jugs
Measure precisely with unmarked jugs.
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Eight Queens
Place queens so that none attack each other.
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Knight’s Tour
Visit every square exactly once with a knight.
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Bridges of Konigsberg
Can you cross every bridge exactly once?
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Magic Square
Arrange the numbers so rows, columns and diagonals share a sum.
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Stone Piles
Take the last stone and you win. Binary numbers reveal the winning plan.
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Icosian Tour
Visit every dot once, then return to the start.
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Four-Color Map
Color neighbors differently.
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Maze Explorer
Carve a maze and compare ways to explore it.
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Shortest Round Trip
Visit every stop and return by the shortest route.
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Shortest Path
Which route really costs the least?
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Four Numbers Make Ten
Combine four digits with plus, minus, times and divide to land exactly on 10.
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Circle Elimination
Standing in a circle and skipping every other person, who is left at the end?
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Hailstone Numbers
Halve it or triple it and add one. How far does a number travel?
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Prime Sieve
Pick a prime and its multiples drop away.
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Grains on a Chessboard
One grain, two, four... What happens by the 64th square?
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Binary Cards
Six cards are enough to guess your number.
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Cutting Squares
Keep cutting squares off a rectangle; the last square’s side is the greatest common divisor.