In case of commodity 'B' the ratio of change in pirce `(DeltaP)` to original price (P) is (-) 0.4. if price elasticitly of demand is (-) 0.5, calculate the percentage change in quantity demanded.

Explanation

Given : `(DeltaP)/P= -0.4` ( Negative value indicates that new price is less than original price , i.e price has decreased . As price is decreasing , the quantity demanded will rise. )
Percentage change in price = `(DeltaP)/P xx 100 = -0.4 xx 100 = -40 % `
Elasticity of Demand `(E_(d))= ("percentage change in Quantity Demanded ")/(" Percentage change in price ")`
`(-) 0.5= ("Percentage Change in Quantity Demanded")/(-40%)`
Percentage change (rise) in Quantity Demanded = 20%