Question:
Max has a utility function U =√ x1x2 where x1 is litres of ice-cream and x2 is boxes of strawberries. The marginal utility of a litre if ice-cream is MU1 =0.5 √x2/ x1 and the marginal utility of a box of strawberries is MU2 =0.5 √x1 /x2. The prices of x1 and x2 are both $2 and Max has a budget of $80.
(a) How much of each good will Max demand?
(b) A fat-tax of $2 per litre is placed on ice-cream so that it now costs Max $4 per litre. Everything else remains the same. How much of each good does Max now consume? How much tax does he pay?
(c) Now suppose that, instead of imposing a $2 tax on ice-cream, the government imposes a $20 income tax, reducing Max's budget to $60. Would Max prefer the $2 tax on ice-cream or the $20 reduction is his budget?
Solution:
U = (x1x2)0.5, P1 = 2, P2 = 2, m = 80
Therefore, the budget equation is:
2x1 + 2x2 = 80
MU1 = 0.5(x2/x1)0.5, MU2 = 0.5(x1/x2)0.5
Therefore, MRS = MU1/MU2 = x2/x1
Setting MRS = P1/P2 = 1, we get,
x2/x1 = 1 => x2 = x1
a) Using the budget equation:
2x1 + 2x2 = 80
- x1 + x2 = 40
- 2x1 = 40
- x1 = 20 = x2
Therefore, he will demand 20 units each of both the goods.
b) Now, P1 = 4
MRS = P1/P2
- x2/x1 = 4/2
- x2/x1= 2
- x2 =2x1
Putting it into the budget equation:
x1 + x2 = 40
- x1 + 2x1 = 40
- x1 = 40/3
- x2 = 80/3
Therefore, tax paid = 40/3 x 2 = 80/3
c) The new budget equation:
x1 + x2 = 60/2 = 30
Putting, x1 = x2 in the budget equation, we get,
- 2x1 = 30
- x1 = 15
- x2 = 15
Utility with fat-tax = (40 x 80/9)0.5 = [40Ö2]/3= 18.86
Utility with income tax = 15
Therefore, Max will prefer the fat-tax on ice cream.