Math Is Fun Forum

Dross

Member

Registered: 2006-08-24

Posts: 325

Reveal the Cards

Below you should see a drawing (if my computer-skills were up to the task, that is) of four cards, each having one half (the left or the right) covered. On the other half, you can see the card is clear or has a circle on it.

We shall number the cards 1, 2, 3 and 4, 1 being the topmost card, 4 being the card on the bottom.

I put to you the following proposition:

If a card has a circle in it's left half, then it also has a circle in it's right half.

Now:

1) What's the least number of cards that must be completely uncovered to see that the proposition is true.

2) Which cards are these?

Last edited by Dross (2007-02-13 02:14:11)

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Bad speling makes me [sic]

Maelwys

Member

Registered: 2007-02-02

Posts: 161

Re: Reveal the Cards

Last edited by Maelwys (2007-02-13 02:20:52)

mathsyperson

Moderator

Registered: 2005-06-22

Posts: 4,900

Re: Reveal the Cards

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Why did the vector cross the road?
It wanted to be normal.

Ricky

Moderator

Registered: 2005-12-04

Posts: 3,791

Re: Reveal the Cards

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"In the real world, this would be a problem.  But in mathematics, we can just define a place where this problem doesn't exist.  So we'll go ahead and do that now..."