A2. Five suspects are being questioned about the order of their arrival at the scene of a crime. They make the following statements.

Aad: "I was the first to arrive."

Bas: "I was the second to arrive."

Carl: "I was the third to arrive."

Dave: "One of Aad and Bas came in before me, and one came in after me."

Erik: "One of Bas and Carl came in before me, and one came in after me."

It is known that exactly one of the suspects is lying.

Who arrived fourth?
A) Aad
B) Bas
C) Carl
D) Dave
E) Erik
A2. E) Erik Aad, Bas, and Carl cannot all have spoken the truth, because then the statements of both Dave and Erik would be false. One of Aad, Bas, or Carl has lied, and therefore the statements of Dave and Erik are true. Aad and Bas cannot both have spoken the truth, because then Dave would have lied, which we just saw is not the case. Similarly, Bas and Carl cannot both have spoken the truth, because Erik's statement would otherwise be false. From the fact that the liar is either Aad or Bas, and at the same time either Bas or Carl, we conclude that the liar must be Bas. Therefore, Aad arrived first and Carl third. Erik came in between Bas and Carl, and that can only be if Bas arrived last and Erik fourth.