求救：有没有好办法?

Numbers 1 through 10 are written on a board. At any time, numbers a, b, c
may be replaced by (2(b + c) − a)/3, (2(c + a) − b)/3, (2(a + b) − c)/3.
Can a number greater than 20 eventually appear on the board?

Thanks

所有跟帖： 

• Impossible. -innercool- ♀ (154 bytes) () 10/23/2009 postreply 21:15:26

• 回复：求救：有没有好办法? -火球魔法- ♂ (258 bytes) () 10/25/2009 postreply 16:31:37

• 多谢大侠们不吝指教。 -cma- ♂ (0 bytes) () 10/26/2009 postreply 08:24:50