A cop arrested four suspects for the bank robbery. When he interviewed them, each made two statements. From his infrared lie-detector he knew that each man made one "true" and one "false" statement. As a result, he soon found out the culprit.

Given the following statements, can you determine who the culprit was?

‘A’ said: “I did not do it. B did.”

‘B’ said: “A did not do it. C did.”

‘C’ said: “B did not do it. I did.”

‘D’ said: “C did not do it. A did.”

Assume A's first statement is false, ie A did it. This means that B's first statement is false, therefore B's second statement is true, ie. C did it. This is impossible, so A's first statement must be true.

Now we know that A did not do it, we can deduce from A's second statement that B did not do it. If B did not do it, C's first statement is true, so C's second statement must be false, which means C did not do it. If none of A, B, or C did it, this leaves only D - or does it?

Unfortunately, it is not stated anywhere that one of these four was definitely the culprit. Therefore, the cop cannot charge any of the four, although he can release A, B, and C. He now needs to find some new evidence to prove it was D, or he needs to find the real culprit.

Posted by matt on 2003-02-03 11:22:47