In the figure given below, AB is the chord of a circle with center O. AB is extended to C such that BC = OB. The straight line CO is produced to meet the circle at D. If ACD = y degrees and AOD = x degrees such that x = ky, then the value of k is

A vertical tower OP stands at the center O of a square ABCD. Let h and b denote the length OP and AB respectively. Suppose APB = 60^o then the relationship between h and b can be expressed as

Three horses are grazing within a semi-circular field. In the diagram given below, AB is thediameter of the semi -circular field with centre at O. Horses are tied up at P, R and S such that PO and RO are the radii of semi -circles with centers at P and R respectively, and S is the centre of the circle touching the two semi -circles with diameters AO and OB. The horses tied at P and R can graze within the respective semi -circles and the horse tied at S can graze within the circle centred at S. The percentage of the area of the semi-circle with diameter AB that cannot be grazed by the horses is nearest to