OpenPuzzle — free mathematical puzzles for grades K

OpenPuzzleOpenPuzzle.org makes mathematical puzzle apps that simultaneously engage the brilliant child and the struggling adult. Their quality comes not from flashiness or addictive reward loops but from the intellectual joy of solving something challenging. The puzzles are free and without ads.Sixteen puzzles are published. Each one opens in a browser with nothing to install and nothing to sign up for, keeps your progress on your own device, and carries on working when the connection does not. Several are classroom puzzles by Gordon Hamilton of MathPickle, implemented here with his rules intact.By subject

Counting and estimating puzzles — How many, how far, how big — and what comes next

Addition and subtraction puzzles — Putting numbers together, and taking them apart

Multiplication and division puzzles — Groups, arrays, factors and sharing out

Fraction puzzles — Parts of a whole, and how they compare

Shape, symmetry and area puzzles — Symmetry, tiling, area, and fitting things together

Logic puzzles — Working it out with nothing left to guess

All sixteen puzzles

Stained Glass — Skip-counting turned into a picture: the pattern each times table draws across a hundred square.

Finding Zero — Every number turned over says how far zero is, so the hunt closes in by reasoning rather than guessing.

Finding the Longest — The longest road in a tree is found by walking away from anywhere twice — a guess by eye, then a count to check it.

Mondrian Puzzle — Every rectangle painted is a multiplication, and the score is the gap between the biggest one and the smallest.

Picasso Brush — A stroke is only as long as one end number divided by the other, so covering the paper is a hunt for factors.

Disco Balls — Prime factors made visible: a product becomes circles inside circles, so multiplication reads as structure.

Stirring Paint — Deduction with no arithmetic in the way — colours, directions and jumps, worked out until every loop closes.

Hitome's Garden — Every line has just two ways to go, and the walls they make decide which flowers end up sharing a bed.

Kajitsu — Cutting fruit into pieces of a given size and symmetry: every morsel has to fold or spin onto itself.

Slug Salad — Each slug eats a number equal to everything it has eaten before it — addition with a reason to check and go back.

Fractured Fractions — One point cuts the whole picture at once, and every piece has to come out holding the fraction written on it.

Gozen — Your next number is forced, so a prime is always coming — and on a prime only a square nobody watches will do.

Zebra — Herds multiply together, so three threes beat one nine — and a stone left on its own throws itself away.

Balanced Zebra — Both colours have to multiply out to the same number, and then to the largest that shape allows.

Galaxea — Two of the three dice are the sides of a rectangle — and the game is which two, and where to hang it.

Hitome's Paddocks — A sheep is worth the squares in its own field, and the two flocks have to end up worth the same.

Lozenge Land — Read a flat tiling as deep stone, and cut the cheapest stairs that let the water climb it.

This page is an application. If you are reading this text, the puzzles themselves have not loaded — each link above goes to a page describing one puzzle, and from there to the puzzle itself.About OpenPuzzle — who makes it, what it costs, and what it collects.