Only One Person Tells the Truth: The Simple Logic That Solves This Classic Puzzle

The Setup
A handwritten note shows a quick mystery: ONLY one person is telling the truth. Three people—A, B, and C—each make a statement about who “did it.”

The Statements

• A says: “B did it.”
• B says: “Not me.”
• C says: “Not me either.”

The Key Rule

• Exactly ONE statement is true.
• That means the other two statements must be false.

Testing the Claims Like a Real Investigation
1) If A were telling the truth (so B did it)

• Then B’s “Not me” would be false (fine).
• But C’s “Not me either” would be true (because C didn’t do it if B did).
  That would create two true statements (A and C), which breaks the rule.
  So A cannot be the only truth-teller.

2) If C were telling the truth (so C didn’t do it)
Then the culprit is either A or B.

• If B did it, then A becomes true too → more than one truth.
• If A did it, then B becomes true too → more than one truth.
  So C cannot be the only truth-teller.

3) If B is telling the truth (so B didn’t do it)

• Then A’s “B did it” is false (good).
• To keep only one truth, C’s “Not me either” must be false, meaning C actually did it.
  Now we have:
• A is false ✅
• B is true ✅
• C is false ✅
  That matches the rule perfectly: ONLY one tells the truth.

The Correct Answer
✅ C DID IT.

Why This Answer Is Guaranteed
Because B being the only truthful speaker is the only scenario where the other two statements can both be false at the same time—forcing C to be the culprit.