Alan, Ben, Chris, Dave and Emma are eating a big cake, once again. After eating, there was one slice left, and they decided to leave it for Frank but someone ate it! Frank asks each person who ate the cake and they said:
Alan said: "It wasn't Ben. It was Chris."
Ben said: "It wasn't Alan. It was Dave."
Chris said: "It wasn't Dave. It wasn't Ben."
Dave said: It wasn't Emma. It was Alan."
Emma said: "It wasn't Chris. It was Dave."
If exactly 5 of the sentences are true, who ate the cake this time?!
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Let us assume who ate the cake one by one and check the number of statements that are true. For example, if Alan ate the cake, then the first statement of Alan was true and the second one is false; both statements of Ben were false; both the statements of Chris were true and so on. And doing the same with Ben, Chris, Dave and Emma. We assign a true statement with 1 and false one with 0, we get the following table.
From the table we see that only if Emma ate the cake that we have exactly 5 true statements.