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David K.H. Begg, Gianluigi Vernasca-Economics-McGraw Hill Higher Education (2011)

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4.2 Price, quantity demanded and total expenditure<br />

(a) Inelastic demand<br />

(b) Elastic demand<br />

D<br />

QI P1<br />

"'<br />

'i:<br />

a.<br />

S'<br />

QI<br />

"'<br />

'i:<br />

a.<br />

P1<br />

P2<br />

s<br />

s<br />

Ql<br />

Quantity<br />

In each case, the supply curve fluctuates between SS and S'S'. In case (a), demand is inelastic, and supply shifts lead<br />

to large changes in equilibrium price but little change in equilibrium quantity. In case (b), demand is elastic, and the<br />

same supply shift now leads to large changes in equilibrium quantity but little change in equilibrium price.<br />

Figure 4.3<br />

The effect of demand elasticity on equilibrium price and quantity fluctuations<br />

Case A<br />

Case B<br />

Case C<br />

QI<br />

"'<br />

'i:<br />

a.<br />

PA -------------------<br />

( -)<br />

I<br />

QI "' PA ------------<br />

'i:<br />

a. (-)<br />

Pa ------------<br />

(+)<br />

P a<br />

- - - - - - - - - - - - - - - - - - - - - - - -<br />

Quantity<br />

0 QA Qa<br />

Quantity<br />

0<br />

QA<br />

Qa<br />

Quantity<br />

When the price is reduced from PA to P6, expenditure changes from OPAAQA to OP6BQ6• Spending rises when demand is<br />

elastic (case A), falls when demand is inelastic (case B), and is unchanQed when demand is unit elastic (case Cl.<br />

Figure 4.4<br />

Elasticity of demand and the effect of price changes on expenditure<br />

73

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