August 2016

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Ponder This Challenge:

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.

Update (4/8): To get a '**' find a solution for the minimal N.

We will post the names of those who submit a correct, original solution! If you don't want your name posted then please include such a statement in your submission!

We invite visitors to our website to submit an elegant solution. Send your submission to the ponder@il.ibm.com.

If you have any problems you think we might enjoy, please send them in. All replies should be sent to: ponder@il.ibm.com