← Economics Fundamentals for Practitioners
Lesson 2 of 3

What Is Supply and Demand?

EconomicsBeginner

Two Curves, One Price

Demand is how much buyers want at a given price - usually more at lower prices. Supply is how much producers are willing to offer at a given price - usually more at higher prices. The price where the two meet is the equilibrium: the point nobody wants to change.

A price change moves you along a curve. A shift of the whole curve is caused by something else changing - a new competitor entering, a shortage of raw materials, a change in what buyers want.

This shows up at work constantly: why scarce, in-demand skills command higher pay, why cloud compute prices drop as supply scales up, why a sudden feature request from every customer at once strains a team's capacity.

The Formula Behind the Curves

Both curves can be written as simple linear equations in quantity and price, and equilibrium is just the point where they're equal - which means you can solve for it with algebra instead of squinting at a graph.

text
Demand: Qd = 100 - 2P     (people want less as price P rises)
Supply: Qs = 20 + 3P      (producers offer more as price P rises)

Equilibrium is where Qd = Qs:
  100 - 2P = 20 + 3P
  80 = 5P
  P = 16

Plug back in: Qd = 100 - 2(16) = 68, Qs = 20 + 3(16) = 68 -- they match.

Movement ALONG a curve vs. a SHIFT of the whole curve is the single most common point of confusion here. If the price of coffee beans changes, that's a movement along the existing supply curve - producers respond to the new price. If a frost destroys half the coffee crop, the entire supply curve shifts left (less is offered at every price, not just the current one) - a genuinely different kind of change with a different graph.

This plays out in tech constantly: cloud compute pricing tracks supply and demand almost literally, with providers running "spot pricing" that rises and falls with real-time server demand. And it's the direct reason a specialized, scarce skill (say, a narrow area of ML infrastructure) commands a premium salary - demand from companies is high relative to the supply of people who can do it well, full stop.