Digital PSAT Math Practice Question 315: Answer and Explanation

Question: 315

A lamp business uses the following equations to express supply and demand as a function of price and quantity for its lamps:

Supply: Price = 30 – Quantity
Demand: Price =10 + 3 × Quantity

How many lamps does the business need to sell in order for the supply of lamps to equal the demand for lamps exactly-i.e., for the supply and demand to be at equilibrium?

Grid-In:

Correct Answer: 5

Explanation:

5 Since the supply and demand are at equilibrium, set the two expressions equal to one another and solve for the number of lamps:

30 - Quantity = 10 + 3 × Quantity 20 = 4 × Quantity 5 = Quantit y
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