n次可称（3^n-3）/2个，并指出它是过轻或过重。

如果另外有一个好球，或者不需要知道过轻或过重，n次可称（3^n-1）/2个。

所有跟帖： 

• 康MM的公式正确, 3次只能称12个球,而4次能称39个球. -Blue_Diamond- ♂ (21 bytes) () 05/02/2010 postreply 09:49:20

• 3 times are enough for 13 balls -jinjing- ♀ (263 bytes) () 05/02/2010 postreply 12:30:37

• 回复：3 times are enough for 13 balls -wushuihe- ♂ (93 bytes) () 05/02/2010 postreply 15:39:14

• not big deal,careless,3 times are enough for 13 balls -jinjing- ♀ (273 bytes) () 05/02/2010 postreply 18:03:21

• 回复：not big deal,careless,3 times are enough for 13 balls -wushuihe- ♂ (25 bytes) () 05/03/2010 postreply 01:52:46

• 4 times are enough for4 2 ,but you need 5 times. -Jinjing- ♀ (109 bytes) () 05/02/2010 postreply 14:03:37

• 4 times are enough for 42 balls, you need 5 times. -jinjing- ♀ (168 bytes) () 05/02/2010 postreply 14:12:59

• 回复：4 times are enough for 42 balls, you need 5 times. -康MM- ♀ (123 bytes) () 05/03/2010 postreply 03:59:22