I’m on holiday in the lovely country of Philitaly, and planning to send plenty of postcards because postage is very cheap. But the country only allows up to three stamps on any letter.
Can you tell me which three denominations of stamps would allow me to cover any cost of postage from 1 cent to 15 cents inclusive?
And which four stamp denominations would allow all values from 1 to 24 cents?
Answer next week
#23 Circling the squares
Solution
We are told that one of 18’s neighbours is 15. The other neighbour can’t be 7 (because 18+7=25), so 7…
Solution
We are told that one of 18’s neighbours is 15. The other neighbour can’t be 7 (because 18+7=25), so 7…
Article amended on 21 October 2019
• There turns out to be at least one other rearrangement of a dartboard in which each neighbouring pair adds up to a square number: 20, 18, 15, 10, 6, 19, 17, 8, 1, 3, 13, 12, 4, 5, 11, 14, 2, 7, 9, 16.
