Suppose the domestic supply (Q^S) and demand (Q^D) for skateboards in the United States are given by the following set of equations: $$\begin{array} { l } Q ^ { S } = - 60 + 3 P \ Q ^ { D } = 390 - 2 P \end{array}$$ In the absence of international trade in skateboards how many skateboards will be sold in the United States? A)138 B)258 C)210 D)930

Question

Quizplus · Accepted Answer

To find the equilibrium quantity sold in the absence of international trade, set the supply equation equal to the demand equation and solve for $P$, then substitute $P$ back into either the supply or demand equation to find $Q$. $$Q^S = Q^D$$$$-60 + 3P = 390 - 2P$$$$5P = 450$$$$P = 90$$Substitute $P = 90$ into either equation, for example, the demand equation:$$Q^D = 390 - 2(90) = 390 - 180 = 210$$Therefore, 210 skateboards will be sold in the United States in the absence of international trade.

Suppose the Domestic Supply (QS) and Demand (QD) for Skateboards QS=−60+3PQD=390−2P\begin{array} { l } Q ^ { S } = - 60 + 3 P \\Q ^ { D } = 390 - 2 P\end{array}QS=−60+3PQD=390−2P​

Suppose the Domestic Supply (Q^S) and Demand (Q^D) for Skateboards $\begin{array} { l } Q ^ { S } = - 60 + 3 P \\Q ^ { D } = 390 - 2 P\end{array}$