The cross-price elasticity between goods X and Y is -0.8. If the price of Y rises by 20%, the quantity demanded of X will change by:

1. Use $E_c = \dfrac{\%\ \text{change in quantity of } X}{\%\ \text{change in price of } Y}$. 2. Rearrange: % change in $X = E_c \times \%$ change in price of $Y$. 3. Substitute: $-0.8 \times 20\% = -16\%$. 4. The negative sign means quantity of X falls by 16% (X and Y are complements). _Source: ICAI BoS CA Foundation Paper 4 Business Economics, Ch 2 Unit I "Law of Demand and Elasticity of Demand", p.35_