FILE No.49Unsolved
A diamond was stolen from a museum display case. The stone had been cut into a cube measuring 1 cm on a side, so its volume is 1 cubic centimeter. The weight measured before the exhibit was 3.5 grams.
A few days later, a "diamond" was returned to the display case. It looked exactly the same in shape and size. But when it was weighed again, it came to only 2.5 grams.
The density of diamond is about 3.5 grams per cubic centimeter. The density of glass is about 2.5 grams. Other gems have densities different from these.
What is the returned "diamond"?
If you get stuck, open the hints one at a time, in order.
Does weight change with the material even for things of the same size?
How many grams was the returned stone?
What material matches that weight?
What is the returned "diamond"?
Choose the answer closest to the truth.
A fake made of glass
The answer is a fake made of glass.
If the size is the same (1 cubic centimeter) but the weight differs, the material differs. Diamond is about 3.5 grams and glass is about 2.5 grams. The returned stone is 2.5 grams, which matches the density of glass exactly.
If it had been ground down to make it lighter, its shape and size would have changed. When the look is the same and only the weight is lighter, the material has been switched.
Because the shape and size look the same, you find it hard to imagine a switch.
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