Logic puzzles and brain teasers

After toggling 100 doors in a pattern, which doors remain open at the end?

Albert knows the month, Bernard knows the day. Can you determine Cheryl’s birthday from their conversation?

The first passenger sits randomly. What is the chance the last passenger gets their own seat?

100 prisoners are isolated, but one light switch may let them prove everyone has visited the room.

Three guests pay for a room, but a strange calculation seems to make one dollar disappear.

You can race only 5 horses at a time and have no stopwatch. How many races are needed to find the fastest 3?

Can 31 dominoes cover a chessboard with two opposite corners removed?

Five pirates must divide 100 gold coins. What should the smartest pirate propose to survive and keep the most?

With only 2 eggs, what is the minimum number of drops needed to guarantee finding the critical floor?

One of 8 chocolate bars is poisoned. With only 2 testers, can you identify it in one round?

One guard always lies, one always tells the truth. Which door leads to freedom?

100 prisoners may each open 50 boxes to find their own number. Can a strategy save them all?