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Slightly off topic: The bag-of-potatoes puzzle could trip some people up. The stated problem is: “You have a 100 pound bag of potatoes. 99% of the bag is wat
by dctoedt 17y ago
Slightly off topic: The bag-of-potatoes puzzle could trip some people up.
The stated problem is: “You have a 100 pound bag of potatoes. 99% of the bag is water weight. You leave the bag in the sun for a few hours. Now you bring it in and it is only 98% water weight, due to evaporation. What is the new total weight of the bag of potatoes?”
The first-reaction answer is that the bag now weighs 98 pounds. But originally the bag contained 1 lb of solid, 99 pounds of water. (Let's assume no other liquids than water). After evaporation, you still have 1 lb of solid, but it's now 2% of the total weight. For 1 pound of solid to equal 2% of total weight, the total weight has to be 50 pounds. That means the bag has only 49 pounds of water remaining. (That seems like a lot of evaporation for just a few hours in the sun.)
- pavel_lishin 17y agoI don't understand how you reached the conclusion that the 1lb of solid becomes 2% of the total weight after evaporation. Seems to me that it would be 1.01%.
- dctoedt 17y agoThe statement of the problem says that, after evaporation, the bag is now 98% water by weight, meaning that the solid matter is now 2% (100% - 98%) instead of the 1% it started out as. Per the problem statement, the 100-pound bag was initially 99% = 99 pounds of water. The non-water part (which we'll assume for simplicity was non-volatile solids) was therefore 100 pounds - 99 pounds = 1 pound. Solids don't evaporate, so even after evaporation, the 1 pound of solid matter remains. That 1 pound is now 2% = 1/50 of the weight, per above. The total weight after evaporation is therefore 50 pounds.
- pavel_lishin 17y agoAh, I see. I'm slow.