Dissatisfied politicians in both Blue and Red parties have decided to set up the Magenta party. When a former member of the Blue party joins the Magentas, there is a 90 per cent chance that the next person to join will also be a former Blue. When a former member of the Red party joins the Magentas, however, the chance is 75 per cent that the next new member will also be a former Red. As the Magenta party grows, what is the proportion of members who used to belong to the Blue party?

Today’s #PuzzleForToday has been set by Dr Russell Gerrard, Associate Professor of Statistics, Faculty of Actuarial Science and Insurance, Cass Business School