In: Economics
A consumer has his preferences represented by the utility function U(x,y) = min {5x + 4y, 4x + 7y} if x is on the horizontal axis and y is on the vertical axis, what is the slope of his indifference curve at the point (10,10)
a. -4/7
b. -5/4
c. -4/5
d. -7/4
e. -5/7
Utility function is given by :
U(x,y) = min {5x + 4y, 4x + 7y}
Now at (x,y) = (10,10) we have U = U(x,y) = min {5*10 + 4*10, 4*10 + 7*10} = 90 which lies on segment 5x + 4y (Because at 10,10 this segment will have lower value)
So equation of indifference curve at 10,10 will be U = 5x + 4y = 90 => y = (1/4)(90 - 5x)
Slope = dy/dx = (1/4)*(-5) = -5/4
Thus, Slope of indiference curve at (10,10) is -5/4
Hence, the correct answer is (b) -5/4