Today’s puzzle is a trip.
You are in a big city where all the streets go in one of two perpendicular directions. You take your car from its parking place and drive on a tour of the city such that you do not pass through the same intersection twice and return back to where you started. If you made 100 left turns, how many right turns did you make?
I’ll be back with the answer at 5pm UK.
PLEASE, NO SPOILERS.
Today’s puzzle comes from the Russian maths competition, the Tournament of the Towns, from the Senior O-level paper, Spring 2005. Thanks to Carlos D’Andrea of the University of Barcelona for suggesting it.
One recent column introduced readers to Sandwich Sudoku, a really fun new sudoku variant. The Guardian now has a sandwich sudoku every Saturday in the printed paper. But if you wanted to play it online, the first Sandwich Sudoku app is now up and running, available at the AppStore and Steam. More info here.
I set a puzzle here every two weeks on a Monday. I’m always on the look-out for great puzzles. If you would like to suggest one, email me.
I’m the author of Football School, a book series for 7 to 12 year olds that opens up the curriculum through football. The latest in the series, Football School Season 4, is out next week but you can preorder now. It contains chapters on the links between football and classical music, spitting, magic, timekeeping, the International Space Station, etymology and much much more.
Finally, I went to see Hail Satan? this weekend. If you are interested in philosophy, rational thought, science, activism and politics, and have a sense of humour, you’ll love this film.
