Can you solve it? Are you smart enough to work for Elon Musk?

Musk liked to set job applicants a problem.

You are on the ground. One mile south, one mile west and one mile north. Exactly where you started is where you end up. Do you know where you are?

The answer was the North Pole. The question is not new. 1824 is the earliest known reference to a version of this puzzle.

Musk would ask "Where else could it be?" according to his biographer.

This is the first puzzle of the day.

There are many excellent puzzles because of the shape of the Earth. Three of them are here.

This is the first thing. There is one direction.

You are on the ground. You travel for 10 miles in a straight line. You travel another ten miles in a straight line after a quick stop. Exactly where you started is where you end up. Do you know where you are?

There are two The circle was squaring.

You are on the ground. Ten miles north, ten miles west, ten miles south and ten miles east. Exactly where you started is where you end up. Do you know where you are?

This is a real question. Most starting points won't get you back to where you started.

If you think you have an answer, I will ask Musk to find another place to build it.

There are three. It's called brain fog.

Phileas Fogg left London on October 2, 1872 in Jules Verne's Around the World in Eighty days. He travels through Egypt, India, Japan, the US and the Atlantic. The book says the trip takes 80 days. He arrived back in London.

There is an eightieth day after October 2.

Clarifying for pedantic astronomy, geographers and physicists, the Earth is a perfect sphere.

I will return to the UK at 5pm with the answers.

There's noSPOILERS. The shape of the world is something that should be discussed.

I put a puzzle here on Mondays. I like to look for puzzles. Email me if you want to suggest one.

I'm the author of several books of puzzles and children's books. The greatest ever quiz book is out now.

I give talks about math and puzzles to schools. Please let us know if your school is interested.

The puzzle was adapted from one by David Singmaster.