Five marbles of descending sizes are placed in a conical funnel. Each marble is in contact with the adjacent marble(s). Also, each marble is in contact all around the funnel wall.

If the smallest marble has a radius of 8mm, and the largest marble has a radius of 18mm, what is the radius of the middle marble?

Bonus question, suggested by "Juggler": what's the angle of the funnel walls?

Okay, so this seems really easy to me, maybe I'm missing something... But there are five marbles and the difference in radii between the smallest and largest is 10... 10/5 is two... because they're all touching the walls etc they must be going down by a constant, right? the 3rd marble is the middle one, so it is 4 greater than the smallest one... which makes it 12mm, right?

Posted by sean on 2005-08-23 02:34:59