Glass Half Full Riddle

Are you up for another riddle? Do you see the glass half empty of half full?

You are in an empty room and you have a transparent glass of water. The glass is a right cylinder, and it looks like it’s half full, but you’re not sure. How can you accurately figure out whether the glass is half full, more than half full, or less than half full? You have no rulers or writing utensils.


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  1. I accidentally read the hints in the RSS feed.

    Tip the glass so the water reaches the lip. If the bottom of the glass is still covered it’s more than half full. If part is exposed, then it’s less that half. If the water surface is at the edge of both ends then it’s exactly half full.

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  2. That would not be very accurate either, due to the surface tension of water. The water will not be perfectly level at the glass/water boundaries.

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  3. Milkmen in India have known solution to this problem for ages. They been using cylindrical 1 Liter measuring cup to give you half liter milk. They fill up the 1 liter cup, and start pouring the milk till they are just able to see bottom of the cup emerge at one corner. That’s it, you got half cup emptied

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  4. Great post! Thanks for information.

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  5. You can just see how far from the tip of your finger the water reaches when your finger is put next to the glass, then compare that length to the empty space in the glass..

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