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Re-numbering the other way gives 82 under 91, under 89 it's 71 and under 80 it's 45.
There are no numbers in the same place with the re-numbering.
But again well done for trying this unusual harder challenge that is purely based on visualising.
If anyone has a further try do send in your solutions.
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?
Investigate the different shaped bracelets you could make from 18 different spherical beads. How do they compare if you use 24 beads?
How many different shaped boxes can you design for 36 sweets in one layer? Can you arrange the sweets so that no sweets of the same colour are next to each other in any direction?