Hello guzzlers.

Every year the German Mathematical Society runs an online puzzle advent calendar for schoolchildren in which a new puzzle appears every day from 1 to 24 December.

This fantastic initiative has been going since 2010 and about 150,000 schoolchildren aged 10-16 now take part. On average of about 80% get each question correct. Sehr gut, ja?

I like the following question – from the 2010 calendar – and not just because the word “elf” in German means 11.

Waldemar the Elf has a job to do: he must collect all the Christmas wish lists from children who live in the Sahara Desert. Starting in Timbuktu, he is able to complete the round trip and return to Timbuktu in six days. But he is an elf, which means he is very small. An elf can only carry a maximum of four days’ worth of elf food. What is the minimum number of elves Waldemar needs to bring with him to complete the trip?

Clarifications: Waldemar can only travel with other elves. Every elf on the trip must eat a day’s worth of elf food every day. Elf food is not available to buy during the trip, but elves can give each other food that they have brought with them. No elf is allowed to leave Timbuktu twice, nor be left stranded in the desert with no food.

The results will let me know if readers of this column are indeed smarter than German 10-year-olds. Come on guzzlers, don’t let me down!

I’ll be back later with the solution, and the results.

UPDATE: The solution and results are now online here.

I post a puzzle here on a Monday every two weeks.

My most recent book is the mathematical adult colouring book Snowflake Seashell Star. (In the US its title is Patterns of the Universe.)

You can check me out on Twitter, Facebook, Google+ and my personal website.

And if know of any great puzzles that you would like me to set here, get in touch.