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How to figure out this quick math/logic question?

Four cards lie on a table; each card is either red or blue on one side and has a triangle or circle on the other side. The following conditional statement supposedly describes the way that the cards are made:

If a card is blue on one side, it has a circle on the other side.

The puzzle is to figure out which cards have to be turned over to find out if this statement is true. Which cards would you choose? Explain your reasoning... If you can answer this correctly with a good explanation, I will give you the best answer.

Update:

Four cards like on a table: A red one... A blue one, a card with a triangle, and a card with a circle

4 Answers

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  • 10 years ago
    Favorite Answer

    I will choose either the blue card, or the card with the circle. Just flipping one of these cards over will prove the condition right or wrong.

    If I flip the blue card and I see a circle, then the conditional statement is correct. If not, it is false.

    Or

    If I flip the card with the circle and I see blue, then the conditional statement is correct. If not, it is false.

    The other two cards don't really play into proving or disproving the conditional statement.

  • Anonymous
    7 years ago

    Actually, everybody else is wrong and I am right because I am always right.

    I'm kidding, of course, although I did come up with a different answer and despite the three-year gap between the date of my answering and the date of the posting, I'd like to test it out.

    You have to test only combinations that might disprove your hypothesis, because if your hypothesis isn't wrong then it must be right. Only one combination, however, really disproves your hypothesis, and that's the one with blue on one side and a triangle on the other. The erroneous assumption of the other people here is that the converse of the statement presented must be tested, that is the assumption that if a card has a circle then it must be blue or else the statement is false. This, however, isn't at all true. In fact, in no way would a card with a circle on one side and red on the other violate the statement. Thus, one does not have to test the red card at all, nor does one need to test the circle, as neither is included in the disproving combination. One does, however, have to test the blue card and the triangle card, because if the blue card were found to have a triangle on its back or the triangle to have a blue backside, then the statement would be false.

    Thus, the answer is the blue card and the triangle card.

  • 10 years ago

    I would need to turn over any card that is either blue or has a circle. This it to see if it has what it is supposed to on the other side. Then I will know if the statement it T or F. I do not need to know what is on the red or triangle cards; it doesn't matter, because the statement says nothing about the red or triangle cards.

    I

  • Anonymous
    10 years ago

    I would turn over every card that is blue. If there was a circle on the back of both of them, then the conditional would be true. If not, then it wouldn't be true. I wouldn't touch the red cards, as they are unrelated. If the cards were facing the other way, (shapes side up) then I would flip over any circles and see if they were blue. If all circles were blue, then the conditional would be true. I wouldn't touch the triangles, as they are unrelated.

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