Question 106
30 military ships are approaching to the island: 10 destroyers and 20 small ships. All ships are arranged in a circle and all distances between neighboring ships are equal. Two battle ships are defending the island. Each of them has exactly 10 rockets. The first battle ship can launch all 10 rockets at the same time, however all 10 targets must be neighboring. The second battle ship can launch all 10 rockets at the same time, however all 10 targets must alternate. Both battle ships launch rockets at the same time (it means that rockets might hit one target). How many destroyers can be saved regardless of how battle ships will launch their rockets?
(Bogdan Rublyov)
(Bogdan Rublyov)