Most adults do not solve algebra on paper daily, but ratios, percentages, and averages appear constantly in budgeting, fitness tracking, and work metrics.
Shopping and sales
Stacked discounts confuse people because they are not additive. A 20% off coupon on an already 30%-off item is not 50% off — you multiply the remaining amounts.
Stacked discount rule
Final price = Original × (1 − first discount) × (1 − second discount)
Cooking and scaling recipes
Doubling a recipe means doubling every ingredient — that is linear scaling. Baking ratios (flour to liquid) matter more than in soups, where small adjustments are forgiving.