試題詳解

108. In a certain game of chance, a square board with area 1 is colored with sectors of either red or blue. A player, who cannot see the board, must specify a point on the board by giving an x-coordinate and a y-coordinate. The player wins the game if the specified point is in a blue sector. The game can be arranged with any number of red sectors, and the red sectors are designed so that 
 , where Ri is the area of the red sector.
Calculate the minimum number of red sectors that makes the chance of a player winning less than 20%.
(A) 3
(B) 4
(C) 5
(D) 6
(E) 7