Answer:
QD=600-40P
Explanation:
The old equation for the demand for pizza is Qd = 300 - 20P
Now because of an increase in the price of a substitute the demand for pizza doubles, in order to find the new equation will multiply the old equation by 2 because the demand has doubled.
300*2=600
20P*2=40P
New equation = 600-40P
We can check whether our new equation is correct or not.
If we assume the price of pizza to be 10 and then put 10 in both the equations the quantity from equation 2 should be double that of equation 1.
Equation 1= 300-(20*10)
=300-200=100
Equation 2 = 600-(40*10)
=600-400=200
AS we can see the quantity doubled on the same price which means our equation is correct.