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Patrick from Woodbridge School gave a very clear explanation of how to work out which weight is heavier, in just two weighings of the balance, when you have been given 9 weights and you are told that one is slightly heavier than the rest:
It is always possible to find the different weight, using a simple method.Daniel from Barclay School then built on this strategy to work out which weight is heavier in just three weighings of the balance when you have been given 27 weights and been told that one is slightly heavier than the rest: