Five knights sit around a round table. Each knight is either a knight who always tells the truth or a knave who always lies. Knight A says, 'Knight B is a knave.' Knight B says, 'Knight C and Knight D are the same type.' Knight C says, 'Knight E is a truth-teller.' Who are the truth-tellers?
Knights A, C, and E are truth-tellers; B and D are knaves.
Test possibilities: If E is a truth-teller, C speaks truth, so E is true (consistent). If C is true, E is true. If A is true, B is a knave. If B is a knave, C and D are different types. Since C is true (truth-teller), D must be a knave. This forms a consistent logical loop.
About this riddle
Logic riddles give you a few facts and ask what must be true. List what you know, cross out what cannot be, and see what is left.
Difficulty: Hard. More like this: Logic riddles with answers or try Einstein's Logic Grid for a different kind of puzzle.
More logic riddles
Three friends—Leo, Maya, and Sam—each wear a shirt of a different color: red, blue, or green. Maya is not wearing red. Leo is wearing the color that is alphabetically first among the three available colors. What color shirt is Sam wearing?
A snail starts climbing up a slick 20-foot vertical wall. Every single day, the snail climbs up 4 feet, but every single night while sleeping, it slips back 3 feet. On which exact day will the snail first reach the top of the wall?
A rare gemstone is stolen from a museum display case. There are three suspects: Leo, Max, and Sam. Security footage proves that the thief is right-handed. Leo is left-handed. Max claims he was asleep at the time of the theft. Sam is an identical twin to Leo, but Sam is right-handed. Who is the thief?
Five runners finish a school marathon, and only these facts survive. Felix finished ahead of Carmen. Nico finished ahead of Felix. Iris finished ahead of Boris. Boris finished ahead of Nico. Who finished fourth?
Five knights stand in a circle. Each knight either always tells the truth or always lies. Knight 1 says, 'Knight 2 is a liar.' Knight 2 says, 'Knight 3 tells the truth.' Knight 3 says, 'Knight 4 is a liar.' Knight 4 says, 'Knight 5 tells the truth.' Knight 5 says, 'Knight 1 is a liar.' How many of the five knights are liars?
A row goes: student, student, pencil, student, student, pencil, student, student. What comes next?