On a table in front of you is a 750 ml decanter, roughly 1/3 full of old, rare and delicious whiskey. You wish to drink it.
Its owner says you can have the rest of the whiskey  that is, if you can accurately measure how much is left using nothing but a ruler.
You can pick up the decanter, but you cannot spill or pour it.
Can you find the remaining volume left in the decanter? How?
Answer (10.24.24)
Assume the decanter has straight sides and a nonconcave bottom (a rarity, yes).
The area (A) of a square or circle is easily found with a ruler.
Measure the height (H) of the whiskey. The whiskey has a volume of AH_{1}.
Invert the bottle and measure the height of the empty bottle space. This volume is AH_{2}.
You don't even need to know the volume of the decanter  although in this case it is helpful to understand how far off your imprecise measurements might be.

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