Jared took a test today on the Introduction to Probability. This test covered most of the concepts that we have looked at over the past few weeks. Following the test, we spent some time looking at the idea of the complement of an event – in other words, if the probability of an event A is P(A) then its complement is P(A') = 1 – P(A). This was in preparation for understanding the Birthday Paradox which states that you only need to have 23 people in a room to have a 50% probability that two people share a birthday. This is not entirely intuitive, most of us tend to think the number of people must be higher. But a straightforward probability calculation shows this to be the case.