An island has only two kinds of inhabitants: Knights, who always tell the truth, and Knaves, who always lie. You meet two islanders, Alex and Blair. Alex says, 'At least one of us is a Knave.' What are Alex and Blair?
Alex is a Knight, and Blair is a Knave.
If Alex were a Knave, his statement that 'at least one of us is a Knave' would be true, which is impossible for a Knave. Therefore, Alex must be a Knight telling the truth. For his statement to be true while he is a Knight, Blair must be a Knave.
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
On a small island, every resident either always tells the truth or always lies. You meet two residents, Leo and Mia. Leo says, 'At least one of us is a liar.' What are Leo and Mia?
A palindrome is a word that reads the same forwards and backwards. If you take a 5-letter English palindrome, remove its first and last letters, and the remaining 3-letter string is also a valid English word, what must the original word be?
A detective interrogates three suspects: X, Y, and Z. Exactly one of them is guilty. X claims: 'Y is the guilty one.' Y claims: 'I am innocent.' Z claims: 'X is lying about Y.' If only the guilty person is lying and the innocent people are telling the truth, who is guilty?
Three travelers need to cross a river using a boat that can hold a maximum weight of 100 kg. Traveler X weighs 100 kg, Traveler Y weighs 50 kg, and Traveler Z weighs 50 kg. How can all three cross to the other side?
A shepherd needs to cross a river with a wolf, a goat, and a cabbage. The boat can only hold the shepherd and one item at a time. If left unattended, the wolf eats the goat, and the goat eats the cabbage. How many one-way trips across the river must the shepherd make in total to transport all three safely?
Two cars start driving toward each other from towns 300 miles apart. Car A travels at 60 mph, and Car B travels at 40 mph. At the exact same moment Car A starts, a remarkably fast falcon flies from Car A's roof toward Car B at 100 mph. When the falcon reaches Car B, it immediately turns around and flies back to Car A, repeating this until the cars crash. What total distance does the falcon fly?