Joint or Complementary Demand:- When to satisfy one want two or more than two goods are demanded together, then such a demand is called joint demand. To take a snap, we need Camera and Film; to write a letter, we need paper, pen and ink etc. Goods which are jointly demanded are known as complementary goods.

Composite Demand: - Composite demand refers to the demand for one commodity in order to satisfy two or more wants. For example, demand for milk is a composite demand. Some people demand milk to prepare cheese, others to prepare curd and still others to prepare sweet meats etc. Total demand for milk is called composite demand.

Direct And Derived Demand: - when a commodity is demanded for its direct consumption it is called direct demand. For example, demand for cold drink when feeling thirsty or demand for woolen blanket when feeling cold. Derived demand refers to the demand for one commodity as a result of demand for another. For example, demand for bricks, cement, lime, timber etc. is derived demand as the same arises out of the demand for a house. Derived demand is another form of joint demand.

Competitive demand: - Demand for substitutes is known as competitive demand. An increased demand for one means reduced demand for the other. Substitutes are those goods which can be used for one another. At a given income, change in the price of one leads to change in the demand for the other. For example, Campa and limca. If price of campa increases then demand for limca will rise


The amount of a good that a consumer is willing to give up for another good, as long as the new good is equally satisfying. It's used in indifference theory to analyze consumer behavior. The marginal rate of substitution (MRS) is calculated between two goods placed on an indifference curve, displaying a frontier of equal utility for each combination of "good A" and "good B". The marginal rate of substitution is always changing for a given point on the curve, and mathematically represents the slope of the curve at that point. For example, a consumer chooses between hamburgers and hotdogs. In order to determine the marginal rate of substitution, the consumer is asked what combinations of hamburgers and hotdogs provide the same level of satisfaction. When these combinations are graphed, the slope of the resulting line is negative. This means that the consumer faces a diminishing marginal rate of substitution: the more hamburgers they have relative to hotdogs, the fewer hotdogs the consumer is willing to give up for more hamburgers. If the marginal rate of substitution of hamburgers for hot dogs is 2, then the individual would be willing to give up 2 hotdogs in order to obtain 1 extra hamburger.


A small fall in the price of a product may lead to a considerable increase in the quantity demanded, but sometimes even a considerable fall in price may not lead to any increase in demand. The degree of responsiveness of demand to small change in price differs from commodity to commodity. Degrees of elasticity of demand are classified into four types:-

Unit Elasticity:
Demand is unit elastic when percentage change in quantity demand and percentage in price are equal. In case of unit elastic demand the demand curve is a Rectangular Hyperbola. In practice it is difficult to find such commodities as have a demand curve whose elasticity is unit throughout.

 Relatively inelastic demand (ed < 1):
 Demand is said to be relatively inelastic or less than unity when proportionate change in demand  is  less than proportionate change in price. In such cases the slope of demand curve falls rapidly.

 Perfectly inelastic demand (ed = 0):
When there is no change in demand as a result of increase or decrease in price then the demand is perfectly inelastic. The demand curve is vertical on OX axis

Perfectly elastic demand (ed = oc):
The demand is perfectly elastic when even a small change in price cause an infinite large change in amount demanded. A small rise in price on the part of a seller reduces the demand to zero. In such cases the demand curve is parallel to OX axis.

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