Asked by Alejandro
Steven has 9 gold coins that are identical in appearance. However, one coin is counterfeit an weighs slightly less that the others. Using a balance scale, how can he find the counterfeit coin in just two weighings?
Answers
Answered by
MathMate
Split the coins into three groups, A, B and C consisting of 3 coins in each group.
Weigh: A--B
1. If A=B, the the counterfeit is in group C
Weigh any two coins in group C and figure out the rest.
2. If A≠B, then the counterfeit is in the lighter group.
Weigh any two coins in the lighter group and figure out the rest.
Weigh: A--B
1. If A=B, the the counterfeit is in group C
Weigh any two coins in group C and figure out the rest.
2. If A≠B, then the counterfeit is in the lighter group.
Weigh any two coins in the lighter group and figure out the rest.
Answered by
bob
what if the counterfeit coin is on the heavier side because it would tip the scales if a normal one was on the lighter side and a normal one plus the counterfeit one was on the heavier side
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