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0 / 60 seg.
One out of 9 otherwise identical balls is overweight. How can it be identified after 2 weighings?
W
_
_
G
H
_
G
R
_
_
P
_
F
3
B
_
L
L
S
_
G
_
_
N
S
T
_
N
_
T
H
_
R
G
R
_
_
P
_
F
3
,
T
H
_
N
Y
_
_
'
L
L
K
N
_
W
W
H
_
C
H
G
R
_
_
P
_
F
3
C
_
N
T
_
_
N
S
T
H
_
H
_
_
V
Y
B
_
L
L
.
P
_
C
K
2
B
_
L
L
S
F
R
_
M
T
H
_
T
G
R
_
_
P
_
N
D
W
_
_
G
H
_
N
_
_
G
_
_
N
S
T
T
H
_
_
T
H
_
R
Clue
WEIGH A GROUP OF 3 BALLS AGAINST ANOTHER GROUP OF 3, THEN YOU'LL KNOW WHICH GROUP OF 3 CONTAINS THE HEAVY BALL. PICK 2 BALLS FROM THAT GROUP AND WEIGH ONE AGAINST THE OTHER
SPLIT THE BALLS INTO 3 GROUPS WITH 3 BALLS EACH. PICK 2 GROUPS AND USE SCALE TO DETERMINE WHICH GROUP CONTAINS THE HEAVY BALL. ONCE THE GROUP IS DETERMINED, PICK 2 BALLS AND USE THE SCALE. IF THEY ARE EQUAL, THE OTHER BALL IS THE HEAVY ONE
TAKE 6 BALLS AND SPLIT THEM INTO 2 GROUPS OF 3 BALLS EACH. USE THE SCALE TO WEIGH THE 2 GROUPS. IF ONE OF THE GROUPS IS HEAVIER THAN THE OTHER GROUP, PICK 2 BALLS FROM THE HEAVIER GROUP AND USE THE SCALE TO WEIGH THEM. IF THEY ARE EQUAL IN WEIGHT, THE OTHER BALL IN THAT GROUP IS THE HEAVY ONE. IF BOTH THE GROUPS ARE EQUAL IN WEIGHT, THEN PICK THE REMAINING 2 BALLS AND USE THE SCALE TO DETERMINE THE HEAVIER BALL
FIRST HE SPLIT THEM IN TO PILES OF 3, 3, AND 2 BRICKS. THEN HE WEIGHS BOTH GROUPS OF 3 WITH EACH OTHER. IF THEY BALANCE HE KNOWS THE BRICK IS ONE OF THE 2 UNWEIGHED BRICKS AND HE CAN WEIGH THEM TO FIND THE HEAVER ONE. IF THE THE STACKS OF 3 BRICKS DO NOT BALANCE, HE WILL WEIGH 2 OF THE 3 BRICKS. IF THEY BALANCE HE WILL KNOW THE BRICK LEFT UNWEIGHED IS HEAVIER, OR IF THEY DO NOT BALANCE, HE WILL FIND THE HEAVIER ONE
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