You are in a warehouse. In the warehouse are a number of sacks of what look like identical gold bars. It doesn’t matter how many sacks — several, at least. It doesn’t matter how many bars are in each sack — plenty.
You’ve been told you can choose and keep one sack of these bars (no mixing and matching — you have to choose one sack “as is.”)
There’s only one problem: every sack except one is filled with FAKE gold bars. They’re just gold-plated iron or something. Only one of the sacks is filled with real gold bars.
To look at the fake bars and real bars side by side, there’s no difference. But the solid gold bars weigh something a little bit different from the gold-plated fakes. Let’s say the fake bars weigh 10 pounds each, and the real ones weigh 10 pounds and one ounce.
In the room with you is a great, big, old-fashioned penny scale. It’s the kind of scale that you stand on (or put something on) and then you put a penny into the slot, and it tells you the weight. The scale is big enough to handle whatever you need it to weigh in the warehouse.
But you only have one penny.
So you are only going to be able to use the scale to obtain one measurement.
Using that penny and that scale, how do you determine which sack you’re going to take home?
Eve Westvik already posted the answer on the News-Ledger Facebook page.
HERE”S THE ANSWER:
The trick is to weigh a different number of bars from each bag, so when you get their total weight, you can tell which bag the real gold must have come from.
For example, take one bar from the first bag, two bars from the second bag, three bars from the third bag, and so on.
Remember, the fake gold bars weigh 10 pounds each. The real ones weigh an extra ounce each. So let’s say you are weighing a total of six bars, and the final weight is 60 pounds, 2 ounces. You know there must be two real gold bars in the mix to account for those two extra ounces. So they must have come from the second bag.