Place four pebbles on the sand in the form of a square. Keep adding as few pebbles as necessary to double the area. How many extra pebbles are added each time?
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!
For this challenge, you'll need to play Got It! Can you explain the strategy for winning this game with any target?
This is a tricky problem to solve...
Congratulations to Jeremy, formerly of Epsom College, who sent in his solution which involves some concise mathematical reasoning combined with a little trial and error: