I'm somewhere on earth. I walk one mile south, one mile west, and one mile north. I end up exactly where I started. Where could I have started?

This puzzle is a classic brain teaser that was asked at Microsoft. It is also one of the favorites of Elon Musk, co-founder of PayPal and Tesla Motors.

This problem appears in my book Math Puzzles Volume 1 (nearly 5 stars on 9 ratings) which contains many interesting brain teasers and math riddles: http://amzn.to/1GhUUSH

See the solution in a blog post - http://mindyourdecisions.com/b....log/2015/05/15/masha

If you like my videos, you can support me at Patreon: http://www.patreon.com/mindyourdecisions

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h/t: http://mashable.com/2015/05/13..../elon-musk-job-inter

If you buy from the links below I may receive a commission for sales. (As an Amazon Associate I earn from qualifying purchases.) This has no effect on the price for you.

I learned about this puzzle from William Poundstone's book "How Would You Move Mount Fuji" which is a collection of many interesting puzzles that were asked at Microsoft. http://amzn.to/1FnSpml

My Books

"The Joy of Game Theory" shows how you can use math to out-think your competition. (rated 4/5 stars on 23 reviews) https://www.amazon.com/gp/product/1500497444

"The Irrationality Illusion: How To Make Smart Decisions And Overcome Bias" is a handbook that explains the many ways we are biased about decision-making and offers techniques to make smart decisions. (rated 5/5 stars on 1 review) https://www.amazon.com/gp/product/1523231467/

"Math Puzzles Volume 1" features classic brain teasers and riddles with complete solutions for problems in counting, geometry, probability, and game theory. Volume 1 is rated 4.5/5 stars on 11 reviews. https://www.amazon.com/gp/product/1517421624/

"Math Puzzles Volume 2" is a sequel book with more great problems. https://www.amazon.com/gp/product/1517531624/

"Math Puzzles Volume 3" is the third in the series. https://www.amazon.com/gp/product/1517596351/

"40 Paradoxes in Logic, Probability, and Game Theory" contains thought-provoking and counter-intuitive results. (rated 4.9/5 stars on 7 reviews) https://www.amazon.com/gp/product/1517319307/

"The Best Mental Math Tricks" teaches how you can look like a math genius by solving problems in your head (rated 4.7/5 stars on 3 reviews) https://www.amazon.com/gp/product/150779651X/

"Multiply Numbers By Drawing Lines" This book is a reference guide for my video that has over 1 million views on a geometric method to multiply numbers. (rated 5/5 stars on 1 review) https://www.amazon.com/gp/product/1500866148/