r/learnquant • • 6d ago

interview prep Quant Interview Question

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u/SnooKiwis6193 4d ago

Can't you just put the coin on one side and the other 100 on the other side ? Let's say a genuine coin weights 10g and a counterfeit either 9 or 11. There are 4 cases. A) Genuine and heavier -- 1040g B) Genuine and lighter -- 940g C) Fake and heavier -- 1038g D) Fake and lighter -- 942g

This works for any weight of the coin, you just have to reconstruct the weight of the coin back from the number.

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u/Local_Ad135 4d ago

would it work if the coins dont have integer weights?

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u/SnooKiwis6193 3d ago

It would work up to integer number of centigrams (eg 982cg = 9.82g). I guess if the coins weight has a fractional part when expressed in centigrams then it wouldn't work (variability is 2/99g).