Boxing Day – The Mathematics of Sales and Discounts

Boxing Day sales involve percentages off and discounts. A 20% off followed by an extra 10% is not 30% off – it’s 1 – (0.8×0.9) = 28% off. The order of discounts matters (commutative? Multiplication is commutative, so same). Also, ‘buy one get one half price’ is equivalent to 25% off if you buy two. The mathematics of pricing includes elasticity (demand vs price), optimisation (maximising revenue), and game theory (price wars). Boxing Day is a festival of applied arithmetic – and a reminder that ‘saving 30%’ means spending 70%.