Written by: Gihan Marasingha, Senior Lecturer, Mathematics, University of Exeter

*Mathematician Gihan Marasingha specialises in setting devilishly difficult number conundrums, including for BBC Radio 4. Can you solve his latest problem?*

Each day for a week, a tennis player is to receive a number of tennis rackets as a gift. She knows that she’ll get a different number of rackets each day and is told exactly how many she’ll receive in total. Using only this information, she deduces that on at least one day she’ll be presented with at least ten rackets. What is the minimum total number of rackets she could receive for her to know this?

*The solution will appear here at 10am on Monday.*

*Gihan Marasingha does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.*