Fred brings home 100 kg of potatoes, which consist of 99 percent water. He then leaves them outside overnight so that they consist of 98 percent water. What is their new weight?
The surprising answer is 50 kg!
https://en.wikipedia.org/wiki/Potato_paradox
100 kg of potatoes, 99% water, means that there's 99 kg of water, and 1 kg of solids. It's a 1:99 ratio.
If the water decreases to 98%, then the solids account for 2% of the weight. The 2:98 ratio reduces to 1:49. Since the solids still weigh 1 kg, the water must weigh 49 kg.