Types of Demand:- Economics Study Notes Part-1- Best Material for SSC CGL, SSC CHSL , RRB

TYPES OF DEMAND 
Cross demand: Demand primarily dependent upon prices of related goods is called cross demand. The complementary goods and substitutes are called related goods. In case of complementary goods like pen and ink demand for good is inversely related to the prices of other goods but the case in substituting goods are just opposite. Demand for substituting goods is directly related to prices. 
Income demand: Demand primarily dependent upon income is called income demand. 
Direct demand: Demand for goods and services made by final consumers to satisfy their wants or needs is called direct demand. For example guest of hotels make the demand for food. 
Derived demand: Demand for goods and services made according to direct demand is called derived demand. 
Joint demand: Demand made for two or more goods and services to satisfy single need or want is called joint demand. 
Composite demand: Demand for a single commodity made in order to use for different purposes is called composite demand. 

Price Elasticity of Demand (Ed): Refers to the degree of responsiveness of quantity demanded to change in its price. 
Ed. = Percentage change in quantity demanded/ Percentage change in price 
Ed. = P/q X Δq/Δp 
P = Original price Q = Original quantity Δ = Change 

Perfectly inelastic demand (Ed = 0) 
This describes a situation in which demand shows no response to a change in price. In other words, whatever be the price the quantity demanded remains the same. 

Inelastic (less elastic) demand (e < 1) 
In this case the proportionate change in demand is smaller than in price. 

Unitary elasticity demand (e = 1) 
When the percentage change in price produces equivalent percentage change in demand, we have a case of unit elasticity. The rectangular hyperbola as shown in the figure demonstrates this type of elasticity. 

Elastic (more elastic) demand (e > 1) 
In case of certain commodities the demand is relatively more responsive to the change in price. It means a small change in price induces a significant change in, demand. 
Perfectly elastic demand (e = ∞) 
This is experienced when the demand is extremely sensitive to the changes in price. In this case an insignificant change in price produces tremendous change in demand. The demand curve showing perfectly elastic demand is a horizontal straight line. 

Cross-elasticity of demand 
The responsiveness of demand to changes in prices of related goods is called cross-elasticity of demand (related goods may be substitutesor complementary goods). In other words, it is the responsiveness ofdemand for commodity x to the change in the price of commodity y. 
ec = Percentage change in the quantity demanded of commodity X/Percentage change in the price of commodity y 
Measures of cross-elasticity of demand 
Infinity - Commodity x is nearly a perfect substitute for commodity y 
Zero - Commodities x and y are not related. 
Negative - Commodities x and y are complementary.