Let the side of the square = a units, the area of the square = a^2 sq units
Area of the 4 semicircles = area of 2 circles = 2 pi r^2 = 2pi (1/2 a)^2
= pi a^2 / 2
Probability of a point in the unshaded square being picked) = area square / area of the total figure = a^2 / (a^2 * pi/2) = 1 / pi/2 = 2 /pi
which is approximately 65%