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Four Way Smarties (Posted on 2004-11-05) |
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You and four other people (who coincendentally are all smarties) are in late testing room where you will take your test where there is a 6 by 6 grid of equally spaced desks with chairs in the same relative spot.
You go into the room after all four smarties have chosen their location. You have a test taking policy where you always want to sit at the midpoint between two smarties. The smarties in the room with you feel the exact opposite way, so their arrangement is always such that no smartie is at the midpoint of two other smarties
However, depending on where the smarties are sitting, you may not be able to sit at the midpoint since in all cases it would always be where there is no chair and desk. (There is a strict no moving desks or chairs rule too.)
How many ways could the current 4 smarties sit such that you couldn't sit at the midpoint of two smarties if reflections and rotations count as well?
How many ways could you not find where you want to sit if there were 5 smarties other than you and reflections and rotations count as well?
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Submitted by Gamer
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Rating: 4.2000 (5 votes)
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Solution:
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(Hide)
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To place smarties such that they don't have a midpoint that is at a table (an integer) one of the coordinates of the distance between the two has to be odd in every case. (The smarties themselves can't "block" you from sitting in a certain spot by sitting where you would otherwise be able to.)
So, they must be at (odd, even) (odd, odd) (even, odd) (even, even)
Since there are 9 of each type and 4! ways for the 4 smarties to sit, there would be 9^4 * 24 or 157464 different ways this could occur.
With 4 smarties, it is possible that this would occur, but with 5 smarties you could always sit at the midpoint because one ordered pair type would have to repeat. This means ther are 0 ways you wouldn't be able to sit at the midpoint of two smarties. |
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