POTATO PARADOX

The potato paradox is a very simple paradox, but many people find it quite surprising, and confusing, or might even refuse to believe it.

Suppose you buy 100 kg of potatoes. Potatoes contain water, of course, and these particular potatoes contain 99% water.

Overnight, some of the water in the potatoes evaporates, so by the morning, the potatoes contain 98% water. How much do the potatoes now weigh?

What was your answer?

Many people guess 99 kg or similar.

The actual answer is 50 kg!

Veridical paradox

A common response is that this isn't a true paradox, it is simply a counterintuitive fact. But, in fact, it is an example of a veridical paradox - a result that is undoubtedly true, but many people find it hard to believe.

The confusion usually arises because we tend to look at the change in the proportion of water, from 99% to 98%, and jump to the conclusion that the amount of water lost is equal to 1% of the total mass. But that isn't correct. It isn't even close.

A moment's thought proves that the answer of 99 kg can't possibly be true. Initially, there is 99 kg of water out of a total mass of 100 kg, so the water percentage is:

If there was 98 kg of water out of a total mass of 99 kg, the water percentage would be:

So the percentage of water wouldn't be 98%, it would still be very nearly 99%.