Types of Elasticity of Demand

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Types of Elasticity of Demand:

1) Income Elasticity:

It refers to the degree  of responsiveness of a change in quantity demanded to a change in the income only, other factors including price remain unchanged. It is expressed as :

`"Ey" = "Percentage change in Qty. Demanded"/"Percentage change in Income"`

`"Ey" = "% Δ Q"/"% ΔY"`




Δ = Represents Change
Q = Orignal demand
Y = Orignal income
ΔQ = Change in quantity demanded
ΔY = Change in income of a consumer

You should know : 
• Positive income elasticity:
Normal goods for which demand  increases with increase in income. 

• Negative income elasticity:
Inferior or goods for which demand  decreases with increase in income of  consumer.

• Zero income elasticity:
Necessary goods for which demand remains constant with increase in income of the consumer.

2) Cross elasticity :

It refers to a change in  quantity demanded of one commodity due to a change in the price of other commodity. (Complementary goods or substitutes)

`"Ec" ="Percentage change in Qty. demanded of A"/"Percentage change in Price of B"`





QA = Original quantity demanded of commodity A
QA= Change in quantity demanded of commodity A
PB = Original price of commodity B
ΔPB = Change in price of commodity B

You should know : 
• Positive cross elasticity :
Substitute goods. Example, tea and coffee.

• Negative cross elasticity : Complementary goods. Example, tea and sugar.

• Zero cross elasticity : Non-related goods. Example, tea and books.

3) Price elasticity :

According to Prof. Alfred Marshall, price elasticity of demand is a ratio of proportionate change in the quantity demanded of a commodity to a given proportionate change in its price only.

`"Ed" ="Percentage change in Qty. demanded"/"Percentage change in Price"`




Q = Original quantity demanded
ΔQ = Difference between the new quantity and original quantity demanded
P = Original price
ΔP = Difference between new price and original price

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