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divde the 12 balls into 3 sets of 4. # x$ L4 I# F8 F! Z6 `
weight any 2 sets.
$ q' d2 z. \: C: y# ?公仔箱論壇if the 2 sets are equal, then you know the heavy one is in the third
$ S9 _7 Y8 j* k. T+ Q- r& G6 @5.39.217.77:8898if one of the 2 is heavier, then the heavy one is in that set
8 `, b- T; [2 u  Y' p3 A) ~6 x6 \) Btvb now,tvbnow,bttvbthen divide the 4 balls into 2.
& t5 n. s7 R- Q# B+ l* E: I( Uweigh them
: t% Z; B& f3 S: \8 l7 V" z! F% vtvb now,tvbnow,bttvband divide the heavier into 15.39.217.77:8898' E" G4 W+ `. @! d& N9 n
and weight them.tvb now,tvbnow,bttvb0 A8 n; R& T  A3 V+ S# O/ |
3 x weighing and get the ans.  5.39.217.77:8898# k- H9 o+ E) q' \) y" C
in less than 15 secs.