## Sphere Packing

### Problem 222

Published on Friday, 19th December 2008, 01:00 pm; Solved by 1281What is the length of the shortest pipe, of internal radius 50mm, that can fully contain 21 balls of radii 30mm, 31mm, ..., 50mm?

Give your answer in micrometres (10^{-6} m) rounded to the nearest integer.