The Guardian – Alex Bellos
“Wednesday is Pi Day, an annual date of celebration in the mathematical community because March 14, or 3/14, using the US convention for dates, looks like 3.14, which is pi to two decimal places. Pi – usually written as the Greek letter π – is the ‘circle constant’. Take any circle you like. Whatever the size, the ratio of its circumference to its diameter is pi. If you want to know more about this numerical marvel, please scroll down. But first, today’s three puzzles.” (more)