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Story:

Three guys A, B and C meet daily to play frisbee. They determined: Always if A doesn't have a frisbee, then B has one. If B doesn't take along a frisbee, then C has one.

Today B hasn't a frisbee.

Question:

Which boys have a frisbee today?

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closed as off-topic by Brandon_J, Omega Krypton, greenturtle3141, Glorfindel, Rubio Jun 22 at 15:03

This question appears to be off-topic. The users who voted to close gave this specific reason:

If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ Well, without even thinking, 'boys' is plural and B doesn't have a frisbee so A and C do. $\endgroup$ – Duck Jun 21 at 18:49
  • $\begingroup$ How is this a puzzle? It’s a direct statement of a textbook style problem with an entirely mechanical solution. We generally don’t allow those. See Are math-textbook-style problems on topic? for more info. $\endgroup$ – Rubio Jun 21 at 20:16
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    $\begingroup$ I'm voting to close this question as off-topic because this is not a puzzle, nor is it related to puzzle-solving. $\endgroup$ – Brandon_J Jun 21 at 21:08
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Solution:

A and C have frisbees

Because:

If A would't has a frisbee then B would has one. And when B has no frisbee, then C has one

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A and C have frisbees.

This follows from the 2nd statement and the contrapositive of the 1st statement. Specifically:

  1. "if A doesn't have a frisbee, then B has one." Therefore, if B doesn't have a frisbee, then A does.

  2. "If B doesn't take along a frisbee, then C has one." Therefore, since B doesn't have one, C also does.

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