### Mindstretching time

Come on, it's Friday. Take a moment to give the leetle grey cells a spot of exercise. (Shut up, Hercule.) You may have heard this problem before. Don't stop reading if it seems familiar, though, we are going way beyond the usual conclusion.

Every morning a man gets into the lift (elevator) on the floor of the high rise block he lives in and rides down to ground level. Every evening he comes home, gets in the lift, rides up to the tenth floor (four floors below his own), gets out and walks the rest of the way. Why?

If you haven't heard it before, think about it for a while before reading on.

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Now an extra piece of information. The man was easily tall enough to reach every button on the lift's control panel. Think about the problem some more. (I throw this in because the conventional 'right' answer is that the man is too short to reach any button higher than the 10th floor. But I'd like to expand your thinking beyond that 'right' answer.)

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There are many possible solutions. The man could want a little exercise, but four floors of stairs are enough. He might suspect his wife of adultery and want to surprise her. He could stop off at a friend's flat four floors below for a drink each evening. And so on. But what if he actually has to get out rather than wants to - surely the conventional solution is now the only one? No. The higher lift buttons could be broken. The owners of the building could charge for each floor you ride up. He only has a ten floor ticket, so he has to walk the rest. Or there is building work going on in the afternoon which restricts the travel of the lift. Feel like arguing with these solutions? The traditional solution is equally frail - whenever there is someone else in the lift, a short person can get to the right floor. Or he could use a stick.

There are two useful lessons here. The first is that a late arriving piece of information can totally change your knowledge base - and it's difficult to give up an established position. The second is to observe just how many solutions there are - and how conditions can be used to question any idea, however valid. And a not so useful lesson - this also demonstrates why Sherlock Holmes style deduction is rubbish: there are always too many variables to strike lucky as often as he does.

If you come across such 'logic problems' in the future,  please look for alternative solutions.

Image from Wikipedia