IBM Ponder This #220 · August 2016

A king receives 10 bags of N golden coins each. Each coin should weigh exactly 10 grams, but some bags contain (only) counterfeit coins that weigh exactly 9 grams each.

If N>=512 then one can identify the counterfeit bags using a single measurement with an accurate weighing scale. (How?)

Our challenge this month is to find a way to identify the counterfeit bags, when we know that there are at most three such bags out of the ten, and when N=174.

Bonus '*' for solving it with even smaller N.

Solution

Best opened after a real attempt

To be added.