A 100-gram potato is 99% water. If it dries to become 98% water, it will weigh only 50 grams.
Even when working with old-fashioned finite quantities, math can lead to strange results. The key to the potato paradox is to closely look at the math behind the nonwater content of the potato. Since the potato is 99% water, the dry components are 1% of its mass. The potato starts at 100 grams, so that means that it contains 1 gram of dry material. When the dried-out potato is 98% water, that 1 gram of dry material now needs to account for 2% of the potato’s weight. One gram is 2% of 50 grams, so this must be the new weight of the potato.