Question

In: Economics

1. The function f(x, y) = ln(x3 + 2) / (y2 + 3) (this function is...

1. The function f(x, y) = ln(x3 + 2) / (y2 + 3) (this function is of a fraction format) :

a.

has a stationary point at (1, 0)

b.

has a stationary point at (0, 0)

c.

has a stationary point at (0, 1)

d.

has no stationary points

2. Which of the following functions don’t have unit elasticity at P = 6?

a.

Demand: Qd = 24 - 2 P

b.

Demand: Qd = 10/P

c.

Demand: log Qd = 100 - 3 log P

d.

Supply: Qs = 5 P

3. For the following total cost function, find marginal cost (MC), average total cost (ATC) and average variable cost (AVC) and then decide which of the following are true. TC = 0.1Q3 - 4Q2 + 80Q + 150 doesn’t implies

a.

MC = 0.3Q2 - 8Q + 80

b.

ATC = 0.1Q2 - 4Q + 80

c.

AVC = 0.1Q2 - 4Q + 80

d.

MC=AVC at Q=20

4. Solve the output production maximizing problem max Q(x, y) = −x3 − 3y2 + 3x2 + 24y where x and y are the necessary inputs. Find the maximum production

a.

48

b.

52

c.

20

d.

50

Solutions

Expert Solution

Given , f(x,y) = [ln(x3 + 2 )]/ (y2 + 3)

The stationary point for a function of two variables lies where the partial derivatives(wr.t xand wrt y ) are zero simultaneously.

Thus df/dx = 3x2 * (y2 + 3) / [[ln(x3 + 2 )]* (y2 + 3) ] = 0

And df/dy = -[ln(x3 + 2 )]* 2y / (y2 + 3) 2 =0

= > 3x2 * (y2 + 3) = 0

And

[ln(x3 + 2 )]* 2y = 0

* Note that the denominators of both the partial derivatives are always positive

= > Either 3x2 = 0 OR (y2 + 3) = 0 or both =0

But y2 >= 0 always hence not possible

Thus 3x2 = 0 = > x = 0………………………….stationary point at (0,0)

Again from [ln(x3 + 2 )]* 2y = 0

= > either [ln(x3 + 2 )] = 0 OR 2y = 0 or both

If [ln(x3 + 2 )] = 0 = > x3 + 2= 1 = > x = -1

And also y = 0

Hence , optionb

2. the elasticity is equal to (dQ/dp)*(P/Q) where P = 6 and Q is the quantity obtained when P=6

All the Functions except c ) logQd = 100 – 3logP has a unit elasticity at P= 6

Function c) on the other hand has an elasticity of 3

Differentiating logQd = 100 – 3logP totally :-

dQd /Qd = -3*dP/P

= > (dQd/dp)*(P/Qd) = -3(Qd/P) *(P/Qd) = -3

3.

Option b is the answer

Since ATC = TC/Q = 0.1Q2 - 4Q + 80 + 150/Q

4. First order conditions are        dQ/dx= 0 and dQ/dy = 0

= >-3x2 + 6x = 0 = > x (6-3x) = 0

Since x is necessary good so x not equal to zer0

Therefore, (6-3x) = 0

= > x = 2

dQ/dy = -6y+24 = 0 => y = 4

Hence max production = -23 – 3*42 + 3*22 +24*4 = -8 – 48 + 12+96 = 52 option B


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