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Adding All Nine
Make a set of numbers that use all the digits from 1 to 9, once and once only. Add them up. The result is divisible by 9. Add each of the digits in the new number. What is their sum? Now try some other possibilities for yourself!
Doodles
Draw a 'doodle' - a closed intersecting curve drawn without taking pencil from paper. What can you prove about the intersections?
Age 11 to 18
Challenge Level
Euler used a graph to explain the possible routes around Old Konisberg.
He represented the land by dots and the bridges by lines joining the
dots. Think about whether there is an even number of bridges or an odd
number of bridges from each piece of land. 
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NRICH is part of the family of activities in the Millennium Mathematics Project.
NRICH is part of the family of activities in the Millennium Mathematics Project.