The Guardian – Alex Bellos
“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 job and return to Timbuktu in 6 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. No elf is allowed to leave Timbuktu twice, nor be left stranded in the desert with no food.”(more)