Problem 015
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As your posts will be visible to the general public you are requested to be thoughtful in not posting anything that might explicitly give away how to solve a particular problem.
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Don't start begging others to give partial answers to problems
Don't ask for hints how to solve a problem
Don't start a new topic for a problem if there already exists one
See also the topics:
Don't post any spoilers
Comments, questions and clarifications about PE problems.
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andy7788
- Posts: 1
- Joined: Mon Feb 08, 2016 9:24 am
Problem 015
The question shows a 2x2=4 square grid. Am I right to assume that the solution to the 2x2 is based on 3x3=9 sides. If so then can you confirm that the solution to the 20x20 question is based on 21x21 sides.
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hk
- Administrator
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Re: Problem 015
Please don't start a new topic for a problem if there already exists one.
War ruins the life and health of untold numbers of innocent children.
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dawghaus4
- Posts: 56
- Joined: Fri Nov 29, 2013 2:22 am
Re: Problem 015
No, that assumption is not needed. There is no need to look at a 21X21 grid to get the number of paths in a 20X20 grid.andy7788 wrote:The question shows a 2x2=4 square grid. Am I right to assume that the solution to the 2x2 is based on 3x3=9 sides. If so then can you confirm that the solution to the 20x20 question is based on 21x21 sides.
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DJohn
- Posts: 90
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Re: Problem 015
It depends what you mean by "sides". If you mean the edges of the squares, then there aren't 9 in the 2x2 grid. There are 12. It is true that the 2x2 grid has 3 vertical lines and 3 horizontal lines, but multiplying those doesn't give the number of anything that I'd call "sides".andy7788 wrote:The question shows a 2x2=4 square grid. Am I right to assume that the solution to the 2x2 is based on 3x3=9 sides. If so then can you confirm that the solution to the 20x20 question is based on 21x21 sides.
The only thing I can see 9 of in the 2x2 grid are the vertices, where those vertical and horizontal lines meet. The 20x20 grid will have 21 vertical lines, 21 horizontal lines, and 21x21 = 441 vertices. And 20x20 = 400 squares, of course.
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Liquid25677
- Posts: 9
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Re: Problem 015
I have a feeling that this problem could be solved easily without checking all the routes, so I've been trying to come up with a formula for a n*n grid, with no success up to now.