Past exam of the mathematics course of the University of Cambridge 2008 iii Paper 40 2 Solution Created 2026-10-03 Updated 2026-10-14
In a price-taking equilibrium, market clearing fixes aggregate consumption at the dividend , so and . Each agent takes this aggregate benchmark as given when varying their own consumption. Let be a common state-price density and their budget multipliers. Marginal pricing givesWrite and . ThenFor fixed , the second left side is continuous and strictly decreasing from infinity to zero, so it determines a unique positive number . Every coefficient in that equation is deterministic. ConsequentlyThis is the relative-consumption share equilibrium. The absolute consumption streams remain random through .
Assuming finite fundamental prices, the ex-dividend price of the productive asset follows from conditional pricing:The initial state-price budget constraints determine the multipliers up to a common normalization:Together with the scalar market-clearing equation these characterize the equilibrium. A common scaling of all is offset by the reciprocal scaling of . At least one redundant budget equation can be removed, since the initial fractions sum to one.
For completeness, define and . The consumption-financing wealth is . Its stochastic exposure and that of are both proportional to . Thus holding units of the productive asset, with no bank-account balance, finances this wealth and consumption. Indeed, the holding's deterministic changes and dividend consumption balance because and .
If all and , market clearing gives for a constant , and is constant. The budget equations then implyFor differentiable , the general equilibrium has short rate and risky-asset total expected return ; its volatility is . These follow directly from and the Itô formula. In the identical-agent case, .