Every day we encounter uncertainty – will the traffic be heavy on your way to the shops, what is the chance of rain, is it likely the power grid will malfunction? Probability helps us to deal with this uncertainty by indicating the chance of events occurring. However, the probability of an event may differ depending on surrounding conditions.

For example, the probability that the traffic will be heavy depends upon the time of day you’re travelling. Similarly the chance of rain depends on the current season and other weather patterns leading up to the day in question. The chance of a power grid malfunctioning also depends on usage; if we’re in the middle of a heatwave then there may be a few more air conditioners being used (and thus draining the system) than during more comfortable conditions.

This video describes the concept of conditional probability and how it may be calculated. It is recommended you are familiar with the content in the Probability videos ‘What are the chances’ and ‘Tree diagrams’ before watching this video.