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You are given eight coins and told that one of them is counterfeit. The counterfeit one is slightly heavier than the other seven. Otherwise, the coins look identical. Using a simple balance scale, how can you determine which coin is counterfeit using the scale only twice?

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Puzzle Admin 3 years 2 Answers 899 views 0

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    First put 3 coins each side if it shows balance both side then put remaining two and which side will down means than coin is heavy.
    Case-2 if puting 3 coins each side we get one side heavy it means heavy coin is on that side so now we have to find heavy from 3 so now out 2 out of 3 on balance scale if equal then remaining one is heavy otherwise which side is heavy that coin will be heavy.

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    There are 8coinns. We can seperate the coins into 3 groups
    8 coins= 3 coins(group1) + 3coin (gr
    oup2) + 2 coins(group3)
    So counterfeit can be definitely in above 3 groups
    Case 1:
    First scale group1 and group 2
    1. If both group weighs the same counterfeit is in 3 rd group
    2. If group2 weighs more, counterfeit in grp2
    3 . Else counterfeit in grp3

    We hav used scale once till now

    If case 1 satisfies……
    1.a now scale 3 rd grp which hav only 2 coins to find counterfeit

    If case2 satisfies
    2.a scale b/w first grp 3 coins. similar to first 3 cases

    If case 3 satifies scale b/w 3 rd group similar to 2.a

    Hence we can find counterfeit using scale 2 tymz

    Best answer

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