Age 14 to 18 Challenge Level:
Aswaath, from Garden International School, Kuala Lumpur, adapted Alison's method and then used a spreadsheet to calculate the sums directly to verify that Alison's method worked.
Well done to Matthew from Westlakes Academy, Andrew from West Island School, Hong Kong, Michael, and Irina from Loughborough High School for their correct solutions. You can read Michael's solution
and Irina's solution