Elasticity Sniper

Goods fall towards three bins at the bottom of the screen. Each card shows what happened in its market, for example Petrol · price +10% · quantity demanded −3%. Work out its elasticity and shoot it into the right bin with 1 2 3 (or ← ↓ →), or tap the bins under the game. The shot always goes to the lowest card, the one in the sights. The bins are always in order: the smallest coefficient on the left.

• Core: price elasticity of demand (PED) and of supply (PES).
• Advanced: waves of PED and PES, then income elasticity (YED), cross elasticity (XED) and a revenue raid, in turn. The bins change between waves.

A good in the wrong bin, or one that reaches the bins, costs a life: you start with 5, and the message shows the working. Each wave is faster than the last, and from the third the numbers are less round.

Price elasticity of demand (PED)

PED = % change in quantity demanded ÷ % change in price. Price and quantity demanded move in opposite directions, so PED is negative; judge it on its size (its absolute value, |PED|). Petrol: −3% ÷ +10% = −0.3.

• Inelastic (|PED| < 1): quantity changes by a smaller percentage than the price. Necessities, goods with few substitutes, and goods that are a small part of income: petrol, cigarettes, bread, salt, electricity.
• Unit elastic (|PED| = 1): quantity changes by the same percentage as the price.
• Elastic (|PED| > 1): quantity changes by a larger percentage. Luxuries and goods with close substitutes: restaurant meals, overseas holidays, one brand of cereal, the petrol at one service station.

Price elasticity of supply (PES)

PES = % change in quantity supplied ÷ % change in price. Price and quantity supplied move together, so PES is positive. Below 1 is inelastic (kiwifruit this season, Auckland houses this year: supply can't grow quickly), exactly 1 is unit elastic, above 1 is elastic (factory-made goods such as T-shirts and plastic bottles, where output can be raised quickly).

Income elasticity of demand (YED)

YED = % change in quantity demanded ÷ % change in income. The sign matters. Below 0: an inferior good, bought less as incomes rise (bus travel, instant noodles). Between 0 and 1: a normal good that is a necessity (milk, toothpaste). Above 1: a normal good that is a luxury (overseas holidays, jewellery).

Cross elasticity of demand (XED)

XED = % change in quantity demanded of good A ÷ % change in the price of good B. The sign matters. Above 0: substitutes (coffee dearer, so more tea). Below 0: complements (petrol dearer, so fewer cars). 0: unrelated.

Revenue raids

Total revenue is price × quantity. When demand is inelastic, raising the price raises total revenue (quantity falls by a smaller percentage). When it's elastic, cutting the price raises it (quantity rises by a larger percentage). When it's unit elastic, neither: total revenue stays the same.

Scoring

A right answer scores 10 in Core and 15 in Advanced, plus up to half as much again for a quick one, and a streak multiplies it (×2 from 4 right in a row, up to ×5). A revenue raid scores 25. A wrong answer, or a card you miss, costs a life and starts your streak again. Scores are checked on the server, so the leaderboards (the world's, and your class's and school's when you're signed in) are fair.

Objective: calculate price, income and cross elasticities from percentage changes, interpret the value and sign of each coefficient, and use PED to predict how a price change affects total revenue.