Сколько королев (ферзей) нужно, чтобы атаковать всю шахматную доску?

Ответ: Пять. Например:

 1 2 3 4 5 6 7 8
 ___ ___ ___ ___ ___ ___ ___ ___
h | | | | | | | | |
 --- --- --- --- --- --- --- ---
g | | | | Q | | | | |
 --- --- --- --- --- --- --- ---
f | | | | Q | | | | |
 --- --- --- --- --- --- --- ---
e | | | | Q | | | | |
 --- --- --- --- --- --- --- ---
d | | | | Q | | | | |
 --- --- --- --- --- --- --- ---
c | | | | | | | | |
 --- --- --- --- --- --- --- ---
b | | | | | | | | |
 --- --- --- --- --- --- --- ---
a | | | | Q | | | | |
 --- --- --- --- --- --- --- ---