I will assume that you want me to answer only question 1 (since all information with regard to question 2 has not been provided).
You're given two demand equations:
and
At equilibrium, quantity demanded equals quantity supplied. So you get the following:
All you need to do is substitute these values of quantity in the price equations and solve for the prices.
and
If I multiply 0.5 to both sides of the second equation, I'll get:
Substituting for 0.5PS in the first equation, I'll get:
Solving the above, you get:
And using this, you find
So the equilibrium price of gold is 1400 and that of silver is 1000.
b) Now if you double the quantity supplied of gold to 150, the two equations you now need to solve to get the prices are:
and
Follow the same steps as before. Multiply 0.5 to both sides of the second equation to get:
Substitute this in the first equation and you have:
Which solves to
And substituting for this in the equation for PS you get:
So, when the quantity supplied of gold rises, you see that the price of both gold and silver fall. The price of gold falls from 1400 to 1300 while that of silver falls from 1000 to 950.
1. Suppose gold (G) and silver (S) are substitutes for each other because both serve as hedges against inflation. Suppose also that the supplies of both are fixed in the short run (QG 75 and Qs 3...