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The demand equation for the Drake GPS Navigator is
x + 4p − 728 = 0,
where x is the quantity demanded per week and p is the wholesale unit price in dollars.
The supply equation is
x − 20p + 1000 = 0,
where x is the quantity the supplier will make available in the market each week
when the wholesale price is p dollars each.
Find the equilibrium quantity and the equilibrium price for the GPS Navigators.
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They want you find the values x and p that satisfy the two given equations SIMULTANEOUSLY.
x + 4p − 728 = 0, (1)
x - 20p + 1000 = 0. (2)
It is easy. From equation (1), subtract equation (2).
The terms with "x" wil cancel each other, and you will get
4p - (-20p) - 728 - 1000 = 0,
or
24p = 1728, ---> p = 1728/24 = 72.
Next, from equation (1) you have, substituting p= 72 there
x + 4*72 - 728 = 0
x - 440 = 0
x = 440.
ANSWER. The solution is x= 440, p= 72.
Solved, with explanations.