Watch Dara Ó Briain: School of Hard Sums Season 1 Episode 5 Online

Dara's back, proving again that mathematics can save the day in almost any circumstance. This week the Mock The Week host tackles problems that you might come across in an Italian restaurant. Comedian David O'Doherty is on hand to help with the puzzles, all set by the fiendishly logical, Oxford university professor, Marcus du Sautoy. The first conundrum comes from counting dough balls. When the menu offers a choice of 6, 9 or 20 dough balls, Marcus wants to know the largest amount of dough balls that cannot be ordered.