German Unity Day – The Mathematics of Reunification

3 October is German Unity Day (1990). The reunification of East and West Germany involved massive economic, social, and mathematical challenges: currency conversion (exchange rates), demographic modelling (migration), and optimisation (infrastructure rebuilding). The ‘Treuhand’ privatisation used linear programming to sell state‑owned enterprises. The mathematics of social choice (voting systems) helped design the new federal structure. Reunification is a case study in applied mathematics – how numbers guide policy and shape lives.