I am a mollusc Remove my first, and I'll make you quite fast Now remove my second, and you won't feel best Now remove my third, and you'll get a square seven Now remove my fourth, and it's lost What am I?

You are given a 5x5 grid with some cells filled with either "X" or "O". Your goal is to fill the remaining cells with "X" or "O" following these rules: Each row and column must contain exactly three "X"s and two "O"s. No adjacent cells (horizontally or vertically) can have the same symbol

Puzzle attribution: Me Goal of Hidato: Fill in a grid with a series of consecutive numbers that connect each other orthogonally or diagonally To get the green checkmark $\color{green}✓$: Solve the puzzle (showing solution process is optional) or show that no solution exists/the solution is n...

This is a word division puzzle which uses cryptic clues. If you're unfamiliar with either or both of those, you can click the associated link. In order to solve the alphametic, you'll first need to fill in the dividend, divisor, and quotient by solving the cryptic clues. I've left the enumeratio...

All twelve pentominoes can be obtained by attaching a single unit square (edge to edge) to one of the squares that make up one (or more) of the following four tetrominos: a) What is the least number of pentominoes required so that all 35 hexomionos can be obtained by attaching (edge to edge) ...

Redrum is a Dutch pirate and when he set foot on an unhabited island he lost his treasure. Or as the Dutch call it his "Schat". Can you figure out what his treasure/"schat" is?

This is a puzzle about (7, 8, 8), or ERIC for short. Can you decode them? IM[K]N, OPQFR ABNP, AC V R[K]T, U R[K]T HIJK L, HIJK JPFH, SFH NPFJ L, NP[J]F V D, EF GF ERIC = ??P??[K] [J]?GFP ?[N]??[K]R