Logic

Bill, a fresh computer graduate from a world-class University, goes for an interview in a software company.


The interviewer is Steve, a grubby old man. And the first question he asks Bill is, 'Are you good at logic?'


'Of course,' replies Bill.


'Let me test you,' replies Steve. 'Two men come down a chimney. One comes with a clean face and the other comes out with a dirty face. Which one would wash his face?'


Bill stares at Steve. 'Is that a test in Logic?' Steve nods.


'The one with the dirty face washes his face', Bill answers wearily.


'Wrong. The one with the clean face washes his face. Examine the simple logic. The one with the dirty face looks at the one with the clean face and thinks his face is clean. The one with the clean face looks at the one with the dirty face and thinks his face is dirty. So, the one with the clean face washes his face.'


'Hmm. I never thought of that," says Bill. 'Give me another test.'


Steve holds up two fingers, 'Two men come down a chimney. One comes out with a clean face and the other comes out with a dirty face. Which one washes his face?'


'We have already established that. The one with the clean face washes his face.'


'Wrong. Each one washes one's face. Examine the simple logic. The one with the dirty face looks at the one with the clean face and thinks his face is clean. The one with the clean face looks at the one with the dirty face and thinks his face is dirty. So, the one with the clean face washes his face. When the one with the dirty face sees the one with the clean face washing his face, he also washes his face. So each one washes one's face.'




'I didn't think of that!' says Bill. 'It's shocking to me that I could make an error in logic. Test me again!'




Steve holds up two fingers, 'Two men come down a chimney. One comes out with a clean face and the other comes out with a dirty face. Which one washes his face?'


'Each one washes his face.'


'Wrong. Neither one washes his face. Examine the simple logic. The one with the dirty face looks at the one with the clean face and thinks his face is clean. The one with the clean face looks at the one with the dirty face and thinks his face is dirty. But when the one with clean face sees that the one with the dirty face doesn't wash his face, he also doesn't wash his face. So neither one washes his face.'


Bill is desperate. 'I am qualified for this job. Please give me one more test!'


He groans when Steve lifts his two fingers, 'Two men come down a chimney. One comes out with a clean face and the other comes out with a dirty face. Which one washes his face?'


'Neither one washes his face', Bill replies, 'I have learnt this logic.'


'Wrong, again. Do you now see, Bill, why programming knowledge is insufficient for this job? Tell me, how is it possible for two men to come down the same chimney, and for one to come out with a clean face and the other with a dirty face? Don't you see the flaw in the premise?'"