#[Demand and supply functions][Funciones de demanda y oferta]#
A
demand function expresses demand $q$ (the number of items demanded) as a function of the unit price $p$ (the price per item). A
supply function expresses supply $q$ (the number of items a supplier is willing to bring to the market) as a function of the unit price $p$. It is usually the case that demand decreases and supply increases as the unit price increases.
Demand and supply are said to be
in equilibrium when demand equals supply. The corresponding values of $p$ and $q$ are called the
equilibrium price and
equilibrium demand.
Example
#[If the demand function for T shirts, measured in the number of shirts sold per day, is $q = -5p+200$, and the supply is $q = 3p - 100$ then equilibrium occurs when demand = supply: ][Si la función de demanda para playeras, medida en el número de playeras vendidas por dí, es $q = -5p+200$ y la función de la oferta se da por $q = 3p - 100$, entonces equilibrio ocurre cuando demanda = oferta: ]#
$-5p+200 = 3p = 100 \implies $ $8p = 100 \implies p = \$12.50.$
#[At that price, one will sell ][A ese precio, se venderá ]# $q = -5(12.50)+ 200 = 137.5$ #[items on average][artículos en promedio]#.