Two spherical balls lie on the ground touching. If one of the balls has a radius of 9 cm, and the point of contact is 10 cm above the ground, what is the radius of the other ball (in centimeters)?
Options
A) 50/4  B) 70/6  C) 80/7  D) 90/8  E) 100/9
A straight line will join the two centers and the point of contact, thus making similar triangles.   1/9 = (r-10)/r   r = 9r - 90   r = 90/8   The answer is 90/8.
<result>D</result>
Two spherical balls lie on the ground touching. If one of the balls has a radius of 9 cm, and the point of contact is 10 cm above the ground, what is the radius of the other ball (in centimeters)?