Truth-tellers and liars — Logical reasoning for kids
Some people always tell the truth and some always lie. Suppose the first person tells the truth and see what follows. If something clashes, they must be a liar. Only one choice survives.
Suppose and check — “assume someone tells the truth, follow what that means, and look for a clash”
Suppose the first speaker is a truth-teller: their words are true. Work out what that says about the others.
Check every statement. A truth-teller’s words must be true; a liar’s words must be false.
If you hit a clash, switch the supposition. The possibility with no clash is the answer.
Use it for: Truth-and-lie puzzles in Olympiads and logic contests, and careful step-by-step thinking.
Worked example: Each person always tells the truth or always lies. Aarav says: “Diya is a liar.” Diya says: “Aarav and I are the same kind.” Is Diya a truth-teller or a liar? Liar
Suppose Aarav tells the truth: Diya is a liar, so her words are false — and they are false, because the two are different kinds. No clash.
Suppose Aarav lies: Diya tells the truth, but then the two are different kinds and her words would be false — a clash. So Diya is a liar.
Check: Aarav truth-teller, Diya liar: both statements fit ✓
Work it out in your head or on paper, type the answer and press Check. Stuck? Press “Show me how”.
Right: 0 · Tried: 0
🏁 Lesson 24 test
20 questions. Check each answer, then go to the next one. Get 16 or more right to pass.
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