Not even twenty minutes. I should know better than to doubt this board.
Two in a similar vein to the OP, very easy once you know what to look for:
You have a big box with 100 oranges. I come and take ten. Then little Johnny comes and takes half that remain. Then little Susie comes and takes twenty two. Finally, little Johnny comes back and puts a third of his loot back in the box. How many apples are left in the box?
You have a big box with 100 oranges. I come and take ten. Then little Johnny comes and takes half that remain. Then little Susie comes and takes twenty two. Finally, little Johnny comes back and puts a third of his loot back in the box. How many oranges do I have now?
I don’t know. You might have already had some before you took ten from me, and you might have eaten some while little Johnny and Suzie were making their transactions.
Or not – these days the Kodiaks/Grizzlies are breeding with the polar bears, so a lot of them aren’t white any more. Also, this works for various points near the south pole too, and since any bear there is obviously a zoo escapee, it could be any color except blinking chartreuse. It mainly depends on the penguin jockey.
Another puzzle linked to on that page is a “lady or a tiger” riddle: http://www.muller.co.il/Riddle/dyn/18/the-king-and-the-blacksmith.aspx#yeshint
-but two of the clues seem contradictory to me. Here’s the relevant info:
Now Room VIII is either empty or has an occupant. If it has an occupant it would be either the princess or a tiger. But it can’t be the princess because then the sign on the room would be a lie; and it can’t be a tiger because then the sign would be true. Therefore room VIII has to be empty, and it’s sign is lying. If it’s lying about room IX being empty, then room IX has an occupant. But then the same contradiction applies to room IX. So where is my reasoning wrong?
254 (I think) pages of jokes, riddles, deep discussions of logical paradoxes and infinite sets and Godel’s thing, not to mention chapter after chapter of truth-teller-and-liar puzzles in umpteen variations, all set in the context of various silly but entertaining stories.
It’s possible for there to be a tiger in room VIII, as long as Room IX is NOT empty. That would make the combined statement “This room has a tiger and Room IX is empty” FALSE, even though the first part is true. Ditto for Room IX: if it has a tiger in it, the sign on Room VI is right.
Oh, you mean the total statement (x AND y) can be false, even though x or y might be true.