I have seen a lot of examples of people who are reasonably well educated (or on their way to being reasonably well educated) who are unable to calculate their way out of a paper bag.

But on the other hand, there was that article about street mathematics from several years ago that said that people could do much more sophisticated math in real life situations than they could in the artificial context of school.

Yet on the third hand (or as we say in this household, “on the gripping hand”), I am totally, completely, and 100% obsessed with a mobile game built on a freemimum model, and almost every post that I see on Facebook comes from members of the online community for this game. The game has various in-game currencies, but the general idea is that you can turn either time or US dollars into in-game diamonds, and then you can turn the diamonds into the things that you want in the game. There are published conversion rates for all of these. A very, very, very large number of posts are asking whether the player can accomplish some goal with the amount of diamonds that she currently has, and if not, how many dollars she would need to spend to achieve this goal.

Who talks about fourth hands? Insects in animated films? There seems to be some perception that when people buy houses that they know exactly how much the mortgage interest deduction saves them each month as well as the present value of that future stream of savings, and they use this information to adjust how much they are willing to pay for homes. Perhaps the fourth hand is the invisible hand?