Ch 4 - Elasticity Of Demand 

  • Price elasticity of demand: measure of the responsiveness of quantity demanded to a price change. if a price is elastic, it is very responsive, if it is inelastic, it’s not responsive
    • Key words:
    • Ed = elasticity of demand
    • Qd = quantity of demand
    • P = price
    • %△ = percentage change
    • Ed = %△Qd / %△P

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  • Steps:

    1. % change in Qd : New quantity - old quantity * 100 Old quantity
    2. % change in price : New price - Old price * 100Old price
    3. %△Qd / %△P
    4. Ignore negative sign

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  • If the answer is:
    • Between 0 and 1: price inelastic demand
    • 1: unitary price elastic demand
    • Above 1: price elastic demand

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  • Inelastic demand curve:

    • When a product’s PED is inelastic and the price falls, the firm will face loss in revenue

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  • Elastic demand curve:

    • When the selling price of a product that has an elastic PED is decreased, the revenue increases (they sell more)

  • Perfectly elastic demand curve:

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  • The PED (price of elasticity of demand) will reduce as the price falls

    • Demand becomes less elastic

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  • Determinants of PED:

    • Availability of substitutes (too many choices)
    • Time
    • Luxury
    • Proportion of income is spent on a good
    • Income elasticity of demand: measures the extent to which the quantity demanded of a product is affected by an income
    • IED = %△Qd / %△ in income

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  • For most normal accounts:

    • Rise in consumer income = rise in demand
    • Fall in consumer income = fall in demand
    • Normal goods = positive YED
    • Normal necessities = income inelastic
    • Normal luxuries = income elastic

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  • Inferior goods: as income rises, demand falls (consumers look for more affordable substitutes)

    • Has negative IED, less than zero
  • Normal goods YED > 0:

    • Increased income = higher demand
    • Positive elasticity
  • Luxury goods YED > 1:

    • Increased income
    • Bigger % increase in demand
  • Inferior goods YED < 0:

    • Increase income leads to fall in demand
    • Negative elasticity

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  • Unitary IED: perfectly proportional, Ey = 1
  • Zero income IED: consumer’s income doesn’t affect demand on product, Ey = 0

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  • An Engel curve shows the relationship between demand for a good (x-axis) and income level (y-axis)

    • Positive slope: normal good
    • Negative slope: inferior good
    • PES price elasticity of supply: a measure of how much the quantity supplied of a product changes when there's a change in its price
    • PES = %△ quantity supplied of the product / %△in price of the product

  • More time being considered = increased elasticity of a product

  • If total costs rise, supply will not be raised

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  • Cross elasticity of demand (XED): measure of how much the demand of a product changes when there's a change in the price of another product

    • XED = %△in quantity demanded of X / %△ in price of product Y
    • If value of XED = positive, goods are substitutes for each other
    • If value of XED = negative, goods are complements of each other
    • If value of XED = 0, goods are unrelated

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