# Math Help - Elasticity of Demand questions

1. ## Elasticity of Demand questions

I'm not sure if I've done this problem correctly.

The problem is:
1. x= -5/4p+20; p=10

How I Solved It:
(-5/4(10))/(-5/4(10)+20)
= -5/3
Is this right or if I've done something wrong, where did I go wrong specifically?

The Other Problem:
2. x= 1/5(225-p^2); p=10

How I Solved It:
x= 45-0.2p^2
(-0.2(10)^2)/(45-0.2(10)^2)
= -20/25
= -0.8
Again, is this right or if wrong, where did I go wrong?

Thanks.

2. ## Re: Elasticity of Demand questions

Hey AntoninaFinn.

Are you just trying to evaluate what x is given p for both questions?

3. ## Re: Elasticity of Demand questions

Originally Posted by AntoninaFinn
I'm not sure if I've done this problem correctly.

The problem is:
1. x= -5/4p+20; p=10
This is ambiguous. Do you mean x= -(5/4)p+ 20 or x= -5/(4p)+ 20?

How I Solved It:
(-5/4(10))/(-5/4(10)+20)
= -5/3
Is this right or if I've done something wrong, where did I go wrong specifically?
Yes, that is correct.

The Other Problem:
2. x= 1/5(225-p^2); p=10

How I Solved It:
x= 45-0.2p^2
(-0.2(10)^2)/(45-0.2(10)^2)
= -20/25
= -0.8
Again, is this right or if wrong, where did I go wrong?
That is NOT what I get. What did you get for the derivative of x with respect to p?
Thanks.[/QUOTE]