Flipping Every N-th

There are 100 face-down cards. The first person that passes by flips over every card, the 2nd person that passes by flips over every 2nd card, and so forth – the n-th person that passes by flips over every n-th…

Street Number Puzzle

You were walking around on a major street with 5-digit street numbers (for example, 11213) and noticed one of the street numbers was special – any two consecutive digits formed a 2-digit perfect square (in the order the digits appeared…

Cryptic Pattern Puzzle

Replace the ?’s in each of these to complete the puzzle: Part 1 “Asia” is H“Cuffs” is S“Ender” is I“Redness” is F“Fuchsia” is ? Part 2 “Using” is E“Desist” is I“Visits” is E“Design” is ? Part 3 “Gross” is W…

Rigging a Vote

There are five candidates participating in an unusual election. There are four rounds of voting, and only two candidates participate in each round, with the winner moving on and the loser dropping out. This means first candidate 1 will run…

Island of Blue Eyes

There is an island known for its people with blue eyes, yet there is at least one green-eyed person on the island. No one knows the color of their own eyes, as there are no reflective surfaces on the island…

Five’s a Crowd

Try to place five points in (or on the perimeter of) an equilateral triangle with side length 10, as to maximize the distance between the points. What is the greatest possible distance between the two closest points?