The blood types we usually talk about are determined by the presence or absence of three antigens (A, B, and Rh-D). Here’s a table, where presence of an antigen is denoted by a 1 (true) and absence, by a 0 (false).

You will reject a blood donation if it contains an antigen that your own blood does not. This is why O- is the “universal donor” (none of those antigens to reject) and AB+ is the “universal recipient” (you have them all naturally, so nothing is rejected). Let’s make a truth table for this, just for the A antigen:

Does that look familiar? It should; it’s the logical implication operation. So a person can receive another’s blood if the donor’s blood type bitwise implies the recipient’s blood type. Neat.

http://finance.yahoo.com/family-home/article/103216/the-cheapest-days-to-buy-certain-items – The cheapest days of the week to buy particular items. Books, clothes, and airplane tickets are my favorites.

http://firedoglake.com/2008/05/24/come-saturday-morning-bike-commuting-for-newbies/ – Bike commuting for newbies. In spite of some interestingly wrong predictions about gas prices at the beginning, it’s full of good information.

http://www.flickr.com/photos/amit-agarwal/3196386402/sizes/l/ – Chart types for different tasks. A great way to pick the most appropriate type of chart for showing the right kind of data.

http://www.sloshspot.com/blog/06-24-2008/Ten-Cool-and-Free-Magic-Bar-Tricks-23 – Ten bar tricks. It’s maaagic!

Now a pair of nerdy ones:

http://www.cs.trinity.edu/About/The_Courses/cs301/math-for-the-layman/ – Math for the layman. Written by the eminent Kenneth Iverson of IBM and APL fame, this is a ground-up course in theoretical mathematics from the basics of numbers to differential and integral calculus.

http://www.linuxalt.com/ – The Linux Alternative Project. This site basically provides a table where one looks up a piece of Windows software whose functionality one wants to replace in a GNU/Linux environment.