Define price elasticity of demand.
It is the measure of the degree of responsiveness of the demand for a good to the changes in its price. It is defined as the percentage change in the demand for a good divided by the percentage change in its price.
`"ed" = "Percentage change in demand for good"/"Percentage change in price of that good"`
`"ed" = (Δ"Q")/(Δ"P") xx "P"/"Q"`
Where ΔQ = Q2 − Q1, change in demand
ΔP = P2 − P1, change in price
P1 = Initial price
Q1 = Initial quantity