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Here's a puzzle that a teacher told me today:

How can you cut twelve in half and get seven?

Hint (only if you're stumped):

Don't let just regular numerals control you

Another Hint

Notice that I didn't use the math tag

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Slice XII across the middle to get VII.

I'm pretty sure that's what Quark's answer is facetiously alluding to.

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  • $\begingroup$ Yep this is what I wanted. Good Job $\endgroup$ – michaelpri Jan 24 '15 at 3:49
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Here's a more mathematical answer from a programmer:

If we use the base 12 numbering system then 12 (in base 12) == 14 (in base 10), and half of that is 7 (in both base 10 and 12).

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    $\begingroup$ Although I think the expected (and now accepted) answer is the Roman Numerical one, I actually like your answer better. +1 from me. $\endgroup$ – BmyGuest Jan 24 '15 at 10:35
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    $\begingroup$ 12 (in base 12 (in base 10)) :P $\endgroup$ – immibis Jan 24 '15 at 11:24
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    $\begingroup$ But the body of the question explicitly spells out t-w-e-l-v-e and s-e-v-e-n. $\endgroup$ – 200_success Jan 25 '15 at 11:13
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    $\begingroup$ @200_success In numeration systems (which happens to be my field of study), we often use "eleven" for what is written as "11" in the base we work in, so "twelve" need not be 2*6 always :) $\endgroup$ – yo' Jan 25 '15 at 19:17
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Cut perfectly in half we have a 7 folks!

Cut perfectly in half we have a 7!

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Slightly different answer:

12 is a base ten number. Cut the base in half, and you get 7.
(base five) 12 = (base ten) 7

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  • $\begingroup$ Now this one is a great way how to think out of the box! $\endgroup$ – yo' Jan 25 '15 at 19:18
  • $\begingroup$ That's brilliant! $\endgroup$ – Behdad Mar 15 '16 at 18:52
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Here's how you can get seven by cutting twelve in half:

enter image description here

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    $\begingroup$ I like this, but it's not what I was looking for. And what happens to the extra part of the one? $\endgroup$ – michaelpri Jan 24 '15 at 3:38
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    $\begingroup$ That isn't cutting 12 in half. Still, nice one! $\endgroup$ – Spikatrix Jan 24 '15 at 3:40
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    $\begingroup$ Doesn't this make 71? $\endgroup$ – KSmarts Jan 26 '15 at 17:32
  • $\begingroup$ Well you do get "a" 7. This is a common puzzle and I wanted to try to be funny instead. $\endgroup$ – Quark Jan 26 '15 at 18:59
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This is 12 points:

. . . .
. . . .
    . .
    . .

Cutting it diagonally from top right to bottom left, we get two sets of 7 points:

. . . .
. . . 

and:

  .
. .
. .
. .
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    $\begingroup$ Before you comment, try halving a single point. $\endgroup$ – cst1992 Jan 7 '16 at 10:15
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@CoolGuy I disagree that it isn't cutting "12" in half. No matter which of the resulting fragments you take, you get 7.

Lines in PS are to ensure that they are exactly (100/100 pixels above and below guide lines) cut in half.

12 / 2 = 7

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    $\begingroup$ But isn't that 77? $\endgroup$ – CodyBugstein Jan 24 '15 at 17:42
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    $\begingroup$ @Imray Nah, it's just two sevens. Two sevens are better than one! $\endgroup$ – Doc Jan 24 '15 at 18:27
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Using roman numbering seems to do the trick : 12 is : XII, cut it horizontally and you have VII at the top

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    $\begingroup$ This has already been answered 3 times $\endgroup$ – michaelpri Jan 25 '15 at 20:33
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    $\begingroup$ I feel like at this point it's a running joke. $\endgroup$ – Quark Jan 25 '15 at 20:40
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12 = XII

strike through the middle

the top half now becomes VII

VII = 7

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protected by Rand al'Thor Mar 7 '15 at 10:57

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