brain teasers Excellent cheap puzzle book: The Moscow Puzzles: 359 Mathematical Recreations Mark Frauenfelder

brain teasers Challenge — can you get these cups unstuck? Mark Frauenfelder

triangles How many triangles do you see? David Pescovitz

numberphile Can you figure out what number comes next? Carla Sinclair

brain teasers Puzzle – how to ensure you get the quarter, not the penny Mark Frauenfelder

riddles Can you solve the seven planets riddle? David Pescovitz

brain teasers Can we wrap a 1x1x1 cube with the blue 3×3 piece of paper, cutting along some edges without disconnecting it? Mark Frauenfelder

brain teasers Can you solve the virus riddle? Mark Frauenfelder

brain teasers A hat puzzle Mark Frauenfelder

brain teasers Brain teaser: draw a cross inside the grid Mark Frauenfelder

brain teasers Puzzle: The Candy Thief Mark Frauenfelder

brain teasers The best place to sit in a "suicide circle" if you really don't want to die Mark Frauenfelder

brain teasers The best book of physics brain teasers Mark Frauenfelder

paradoxes The Missing Dollar puzzle from Martin Gardner's Aha! Gotcha book series Mark Frauenfelder

brain teasers Build this brain-teasing golf ball in a block of wood Mark Frauenfelder

brain teasers Pill-popping panic – a good brain teaser Mark Frauenfelder