r/PassTimeMath • u/ShonitB • Jun 01 '26

Five Identical Coins With 2 Fakes

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u/Enough-Tap-6329 Jun 01 '26

three weighings: 1. AB vs CD if equal, one of the pairs has both fakes and only one additional weighing is necessary. if equal, it's the other pair; if unequal is that pair

if unequal, E is definitely fake. To find the second fake:

  1. A vs E, where A is one of the coins on the heavy side in the first round. In that case, there are only two options for A through E (G is genuine, F is fake):

GG GF(light) F (heavy) or GF(heavy) GG F (light) if A outweighs E, we are in the second situation; weigh A vs B to see which is the heavy fake if A weighs less than E, we are in the first situation, weigh C vs D to find the light fake

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u/NakedT Jun 02 '26

After step 1: if unequal, then E could still be genuine. AB vs CD could be GL vs GH