Who is Speaking The Truth
Before reading ahead, you must know the fact that only one of the people here is telling the truth.
A says that B is lying.
B says that C is lying.
C says both A and B are lying.
Can you find out who is speaking the truth? 
B is saying the truth.
The statements:
(a) A says that B is lying.
(b) B says that C is lying.
(c) C says both A and B are lying.
Check 1: If statement (a) was true (i.e., A is speaking the truth), then ‘B’ must be lying. i.,e, B’s statement that ‘C is lying’ must be false, which, in turn, means that C’s statement must be true. But since C said that both A and B are lying, for c to be true, A must be lying, contradicting the assumption.
Check 2: If statement (c) were true, i.e., both A and B are lying, it means statement A must be false. However, since A’s claim is that B is lying, for it to be false (As per C), B must be saying the truth – that C is lying, which again contradicts the assumption.
As one of the three is speaking the truth, AND both A and C are proven to be false, it implies that B is saying the truth.
If B is saying the truth, then (a) must be false (because A said B is lying), AND C must be lying => statement that both A & B are lying is false, which means either A or B (or both) is saying the truth, which matches A is lying and B is saying the truth.
Your Answer
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