Answer:
Option A, buy less of X and more of Y is correct.
Explanation:
The amount that Mr. Rational is going to spend = $27
Quantity of good X = 5 units
Price of good X (Px) = $3 per unit
Marginal utility of 5th unit of X (MUx) = 30
Quantity of good Y = 6 units
Price of good Y (Py) = $2 per unit
Marginal utility of 6th unit of Y (MUy) = 18
[tex]Now \ find \ \frac{MUx}{Px} = \frac{30}{3} = 10 \\[/tex]
[tex]Now \ \frac{MUy}{Py} = \frac{18}{2} = 9[/tex]
[tex]Since \ the \ \frac{MUx}{Px} is \ greater \ than \ \frac{MUy}{Py}.[/tex]
So good x will be substituted for y in order to reach the consumer equilibrium.
[tex]\frac{MUx}{Px} = \frac{MUy}{Py}[/tex]
Thus, Option a. buy less of X and more of Y is correct.