6563 /www/nrich/html/content/id/6563/ 10 2011-12-12T16:07:05 <mdoxml version="1.0"><p>Fancy something very substantial? Think about one of our challenging open investigations. These will take time and you will need to pose your own questions and make your own mathematical discoveries.</p></mdoxml> 2 3 0 0 0 0 1 Stage 5 Investigations Header Admin Stage 5 Investigation