potato paradox

Etymology
In reference to the 1845 Irish famine, when potatoes became expensive. It has been argued that poorer families, who habitually ate more potatoes, ended up having to consume even more of them, since the higher prices made it even harder to afford any other goods.

Noun

 * 1)  A calculation having a counterintuitive result: "Fred brings home 100 kg of potatoes, which consist of 99% water. He then leaves them outside overnight so that they consist of 98% water. What is their new weight?" The surprising answer is 50 kg.
 * 2)  The paradoxical nature of Giffen goods, where people consume more as the price rises.