1.

A consumer consumer only two goods X and Y and is in equilibrium . Show that when the price of good X rises, the consumer buys less of good X. Use utility analysis.

Answer»

SOLUTION :As , we know condition for consumer equilibrium is ,
Necessary Condition
Marginal utility of last rupeespend on each commodity is same .
Suppose there are two commodities , X and Y respectively.
So , for commodity X , the condition is , Marginal Utility of Money = Price of X
Or, `{:("Marginal Utility of a Product in Util "[MU_x])/("Marginal Utility of One Rupee "[MU_R])=` Price of X
Or `(MU_x)/(P_x) = MU_R ""....(1)`
Similarly , for commodity Y, the condition is ,
`(MU_y)/(P_y)=MU_R ""...(2)`
PUTTING equation (2) in (1) , we GET
`(MU_x)/(P_x)=(MU_y)/P_y`
Putting equation (2) in (1), we get
`(MU_x)/P_x =(MU_y)/(P_y)`
But as given in the questions that the ratio of marginal utility to price in case of X is LOWER than in case of Y.i.e, `(MU_x)/(P_x) lt (MU_y)/P_y` . It is means, marginal utility from the lest rupee spent on commodity X is less than the marginal utility from the last rupee spent on commodity Y . So, to attain the equilibrium the consumer must decrease the quantity of X which will increase the `MU_x` and increase the quantity of Y , which will decrease the `MU_y` . Decrease in quantity of X and increase in quantity of y continue till `(MU_x)/P_x =(MU_y)/(P_y)` .


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