s30z

Divide 3 groups first.
! c) ]6 A2 @3 |: R6 v5.39.217.77i.e. 4 x 4 x 4.
+ }1 C: ^3 G$ W* k% `! CWeight any 2 groups [1st]公仔箱論壇$ a  h, ]4 s1 O9 P( L/ w) K
then you will know the heavier ball in which group.
$ b* |3 k& _; J* z0 j$ AWeight any 2 balls in that group [2nd]
; ?* j- w' c/ m. K% M5.39.217.77then you will know the heavier ball in which 2 balls.
' ?7 \: f2 S( j  uRepeat again in remainders [3rd]
1 s7 [3 [/ F0 L8 k/ `5.39.217.77Got the heavier ball.