7. A circle has its centre at O . A tangent drawn from a point P , which is situated outside the circle, touches the circle at A. If PA = 4 cm & PO=5 cm, then the length of the radius of the circle is
8. An inverted conical shaped vessel is filled with water to its brim. The height of the vessel is 8 cm and radius of the open end is 5 cm . When a few solid spherical metallic balls each of radius 1?2 cm are dropped in the vessel , 25% water is overflowed. The number of balls is:
10. Two circles touch each other internally. The radius of the smaller circle is 6 cm and the distance between the centre of two circles is 3 cm. The radius of the larger circle is